Tag: Dive

Color Inputs: A Deep Dive into Cross-Browser Differences

In this article, we’ll be taking a look at the structure inside <input type='color'> elements, browser inconsistencies, why they look a certain way in a certain browser, and how to dig into it. Having a good understanding of this input allows us to evaluate whether a certain cross-browser look can be achieved and how to do so with a minimum amount of effort and code.

Here’s exactly what we’re talking about:

But before we dive into this, we need to get into…

Accessibility issues!

We’ve got a huge problem here: for those who completely rely on a keyboard, this input doesn’t work as it should in Safari and in Firefox on Windows, but it does work in Firefox on Mac and Linux (which I only tested on Fedora, so feel free to yell at me in the comments if it doesn’t work for you using another distribution).

In Firefox on Windows, we can Tab to the input to focus it, press Enter to bring up a dialog… which we then cannot navigate with the keyboard!

I’ve tried tabbing, arrow keys, and every other key available on the keyboard… nothing! I could at least close the dialog with good old Alt + F4. Later, in the bug ticket I found for this on Bugzilla, I also discovered a workaround: Alt + Tab to another window, then Alt + Tab back and the picker dialog can be navigated with the keyboard.

Things are even worse in Safari. The input isn’t even focusable (bug ticket) if VoiceOver isn’t on. And even when using VoiceOver, tabbing through the dialog the inputs opens is impossible.

If you’d like to use <input type='color'> on an actual website, please let browsers know this is something that needs to be solved!

How to look inside

In Chrome, we need to bring up DevTools, go to Settings and, in the Preferences section under Elements, check the Show user agent shadow DOM option.

How to view the structure inside an input in Chrome.

Then, when we return to inspect our element, we can see inside its shadow DOM.

In Firefox, we need to go to about:config and ensure the devtools.inspector.showAllAnonymousContent flag is set to true.

How to view the structure inside an input in Firefox.

Then, we close the DevTools and, when we inspect our input again, we can see inside our input.

Sadly, we don’t seem to have an option for this in pre-Chromium Edge.

The structure inside

The structure revealed in DevTools differs from browser to browser, just like it does for range inputs.

In Chrome, at the top of the shadow DOM, we have a <div> wrapper that we can access using ::-webkit-color-swatch-wrapper.

Inside it, we have another <div> we can access with ::-webkit-color-swatch.

Screenshot of Chrome DevTools showing the shadow DOM of the <input type='color'>. Right at the top, we have a div which is the swatch wrapper and can be accessed using ::-webkit-color-swatch-wrapper. Inside it, there’s another div which is the swatch and can be accessed using ::-webkit-color-swatch. This div has the background-color set to the value of the parent color input.”/><figcaption>Inner structure in Chrome.</figcaption></figure>
<p>In Firefox, we only see one <code><div></code>, but it’s not labeled in any way, so how do we access it?</p>
<p>On a hunch, given this <code><div></code> has the <code>background-color</code> set to the input’s <code>value</code> attribute, just like the <code>::-webkit-color-swatch</code> component, I tried <code>::-moz-color-swatch</code>. And it turns out it works!</p>
<figure><img src=this issue from 2016. Pre-Chromium Edge apparently doesn’t allow us to style whatever is inside this input. Well, that’s a bummer.

How to look at the browser styles

In all browsers, we have the option of not applying any styles of our own and then looking at the computed styles.

In Chrome and Firefox, we can also see the user agent stylesheet rule sets that are affecting the currently selected element (though we need to explicitly enable this in Firefox, as seen in the previous section).

Screenshot collage of Chrome DevTools and Firefox DevTools showing where to look for user agent styles: Elements > Styles in Chrome and Inspector > Styles in Firefox.”/><figcaption>Checking browser styles in Chrome and Firefox.</figcaption></figure>
<p>This is oftentimes more helpful than the computed styles, but there are exceptions and we should still always check the computed values as well.</p>
<p>In Firefox, we can also see the CSS file for the <code>form</code> elements at <code>view-source:resource://gre-resources/forms.css</code>.</p>
<figure><img src=
Checking browser styles in Firefox.

The input element itself

We’ll now be taking a look at the default values of a few properties in various browsers in order to get a clear picture of what we’d really need to set explicitly in order to get a custom cross-browser result.

The first property I always think about checking when it comes to <input> elements is box-sizing. The initial value of this property is border-box in Firefox, but content-box in Chrome and Edge.

Comparative screenshots of DevTools in the three browsers showing the computed values of box-sizing for the actual input.
The box-sizing values for <input type='color'> compared in Chrome, Firefox and Edge (from top-to-bottom).

We can see that Firefox is setting it to border-box on <input type='color'>, but it looks like Chrome isn’t setting it at all, so it’s left with the initial value of content-box (and I suspect the same is true for Edge).

In any event, what it all means is that, if we are to have a border or a padding on this element, we also need to explicitly set box-sizing so that we get a consistent result across all these browsers.

The font property value is different for every browser, but since we don’t have text inside this input, all we really care about is the font-size, which is consistent across all browsers I’ve checked: 13.33(33)px. This is a value that really looks like it came from dividing 40px by 3, at least in Chrome.

Comparative screenshots of DevTools in the three browsers showing the font values for the actual input.
The font values for <input type='color'> compared in Chrome, Firefox and Edge (from top-to-bottom).

This is a situation where the computed styles are more useful for Firefox, because if we look at the browser styles, we don’t get much in terms of useful information:

Screenshot of what we get if we look at the browser styles where the font was set for Firefox. The value for the font is -moz-field, which is an alias for the look of a native text field. Expanding this to check the longhands shows us empty instead of actual values.
Sometimes the browser styles are pretty much useless (Firefox screenshot).

The margin is also consistent across all these browsers, computing to 0.

Comparative screenshots of DevTools in the three browsers showing the margin values for the actual input.
The margin values for <input type='color'> compared in Chrome, Firefox and Edge (from top-to-bottom).

The border is different for every single browser. In both Chrome and Edge, we have a solid 1px one, but the border-color is different (rgb(169, 169, 169) for Chrome and rgb(112, 112, 112) for Edge). In Firefox, the border is an outset 2px one, with a border-color of… ThreeDLightShadow?!

Comparative screenshots of DevTools in the three browsers showing the border values for the actual input.
The border values for <input type='color'> compared in Chrome, Firefox and Edge (from top-to-bottom).

What’s the deal with ThreeDLightShadow? If it doesn’t sound familiar, don’t worry! It’s a (now deprecated) CSS2 system value, which Firefox on Windows shows me to be rgb(227, 227, 227) in the Computed styles tab.

Screenshot of Computed panel search in Firefox on Windows, showing that the ThreeDLightShadow keyword computes to rgb(227, 227, 227).
Computed border-color for <input type='color'> in Firefox on Windows.

Note that in Firefox (at least on Windows), the operating system zoom level (SettingsSystemDisplayScale and LayoutChange the size of text, apps and other items) is going to influence the computed value of the border-width, even though this doesn’t seem to happen for any other property I’ve checked and it seems to be partially related to the border-style.

Screenshot showing the Windows display settings window with the zoom level options dropdown opened.
Zoom level options on Windows.

The strangest thing is the computed border-width values for various zoom levels don’t seem to make any sense. If we keep the initial border-style: outset, we have:

  • 1.6px for 125%
  • 2px for 150%
  • 1.7px for 175%
  • 1.5px for 200%
  • 1.8px for 225%
  • 1.6px for 250%
  • 1.66667px for 300%

If we set border-style: solid, we have a computed border-width of 2px, exactly as it was set, for zoom values that are multiples of 50% and the exact same computed values as for border-style: outset for all the other zoom levels.

The padding is the same for Chrome and Edge (1px 2px), while Firefox is the odd one out again.

Comparative screenshots of DevTools in the three browsers showing the padding values for the actual input.
The padding values for <input type='color'> compared in Chrome, Firefox and Edge (from top-to-bottom).

It may look like the Firefox padding is 1px. That’s what it is set to and there’s no indication of anything overriding it — if a property is overridden, then it’s shown as grey and with a strike-through.

Screenshot of Firefox DevTools highlighting how the border set on input[type='color'] overrides the one set on input and the look (grey + strike-through) of overridden properties.
Spotting overrides in Firefox.

But the computed value is actually 0 8px! Moreover, this is a value that doesn’t depend on the operating system zoom level. So, what the hairy heck is going on?!

Screenshot of Firefox DevTools showing how the computed padding value on <input type='color'> isn’t the one that was set on input, even if no override seems to be happening.”/><figcaption>Computed value for <code>padding</code> in Firefox doesn’t match the value that was set on input.</figcaption></figure>
<p>Now, if you’ve actually tried inspecting a color input, took a close look at the styles set on it, and your brain works differently than mine (meaning you do read what’s in front of you and don’t just scan for the one thing that interests you, completely ignoring everything else…) then you’ve probably noticed there is something overriding the <code>1px</code> padding (and <a href=should be marked as such) — the flow-relative padding!

Screenshot of Firefox DevTools showing the flow-relative padding overriding the old padding due to higher specificity of selector (input[type='color'] vs. input).
Flow-relative padding overrides in Firefox.

Dang, who knew those properties with lots of letters were actually relevant? Thanks to Zoltan for noticing and letting me know. Otherwise, it probably would have taken me two more days to figure this one out.

This raises the question of whether the same kind of override couldn’t happen in other browsers and/or for other properties.

Edge doesn’t support CSS logical properties, so the answer is a “no” in that corner.

In Chrome, none of the logical properties for margin, border or padding are set explicitly for <input type='color'>, so we have no override.

Concerning other properties in Firefox, we could have found ourselves in the same situation for margin or for border, but with these two, it just so happens the flow-relative properties haven’t been explicitly set for our input, so again, there’s no override.

Even so, it’s definitely something to watch out for in the future!

Moving on to dimensions, our input’s width is 44px in Chrome and Edge and 64px in Firefox.

Comparative screenshots of DevTools in the three browsers showing the width values for the actual input.
The width values for <input type='color'> compared in Chrome, Firefox and Edge (from top-to-bottom).

Its height is 23px in all three browsers.

Comparative screenshots of DevTools in the three browsers showing the height values for the actual input.
The height values for <input type='color'> compared in Chrome, Firefox and Edge (from top-to-bottom).

Note that, since Chrome and Edge have a box-sizing of content-box, their width and height values do not include the padding or border. However, since Firefox has box-sizing set to border-box, its dimensions include the padding and border.

Comparative screenshots of DevTools in the three browsers showing the layout boxes.
The layout boxes for <input type='color'> compared in Chrome, Firefox and Edge (from top-to-bottom).

This means the content-box is 44pxx23px in Chrome and Edge and 44xpxx19px in Firefox, the padding-box is 48pxx25 in Chrome and Edge and 60pxx19px in Firefox and the border-box is 50pxx27px in Chrome and Edge and 64pxx23 in Firefox.

We can clearly see how the dimensions were set in Chrome and I’d assume they were set in the same direct way in Edge as well, even if Edge doesn’t allow us to trace this stuff. Firefox doesn’t show these dimensions as having been explicitly set and doesn’t even allow us to trace where they came from in the Computed tab (as it does for other properties like border, for example). But if we look at all the styles that have been set on input[type='color'], we discover the dimensions have been set as flow-relative ones (inline-size and block-size).

Screenshot of the Firefox user agent styles showing flow relative dimensions being set on input[type='color'].
How <input type='color'> dimensions have been set in Firefox.

The final property we check for the normal state of the actual input is background. Here, Edge is the only browser to have a background-image (set to a top to bottom gradient), while Chrome and Firefox both have a background-color set to ButtonFace (another deprecated CSS2 system value). The strange thing is this should be rgb(240, 240, 240) (according to this resource), but its computed value in Chrome is rgb(221, 221, 221).

Comparative screenshots of DevTools in the three browsers showing the background values for the actual input.
The background values for <input type='color'> compared in Chrome, Firefox and Edge (from top-to-bottom).

What’s even stranger is that, if we actually look at our input in Chrome, it sure does look like it has a gradient background! If we screenshot it and then use a picker, we get that it has a top to bottom gradient from #f8f8f8 to #ddd.

Screenshot of the input in Chrome. A very light, almost white, grey to another light, but still darker grey gradient from top to bottom can be seen as the background, not the solid background-color indicated by DevTools.
What the actual input looks like in Chrome. It appears to have a gradient, in spite of the info we get from DevTools telling us it doesn’t.

Also, note that changing just the background-color (or another property not related to dimensions like border-radius) in Edge also changes the background-image, background-origin, border-color or border-style.

Animated gif. Shows the background-image, background-origin, border-color, border-style before and after changing the seemingly unrelated background-color - their values don't get preserved following this change.
Edge: side-effects of changing background-color.

Other states

We can take a look at the styles applied for a bunch of other states of an element by clicking the :hov button in the Styles panel for Chrome and Firefox and the a: button in the same Styles panel for Edge. This reveals a section where we can check the desired state(s).

Screenshot collage highlighting the buttons that bring up the states panel in Chrome, Firefox and Edge.
Taking a look at other states in Chrome, Firefox, Edge (from top to bottom).

Note that, in Firefox, checking a class only visually applies the user styles on the selected element, not the browser styles. So, if we check :hover for example, we won’t see the :hover styles applied on our element. We can however see the user agent styles matching the selected state for our selected element shown in DevTools.

Also, we cannot test for all states like this and let’s start with such a state.

:disabled

In order to see how styles change in this state, we need to manually add the disabled attribute to our <input type='color'> element.

Hmm… not much changes in any browser!

In Chrome, we see the background-color is slightly different (rgb(235, 235, 228) in the :disabled state versus rgb(221, 221, 221) in the normal state).

Chrome DevTools screenshot showing the background being set to rgb(235, 235, 228) for a :disabled input.
Chrome :disabled styling.

But the difference is only clear looking at the info in DevTools. Visually, I can tell tell there’s a slight difference between an input that’s :disabled and one that’s not if they’re side-by-side, but if I didn’t know beforehand, I couldn’t tell which is which just by looking at them, and if I just saw one, I couldn’t tell whether it’s enabled or not without clicking it.

Disabled and enabled input side by side in Chrome. There is a slight difference in background-color, but it's pretty much impossible to tell which is which just by looking at them.
Disabled (left) versus enabled (right) <input type='color'> in Chrome.

In Firefox, we have the exact same values set for the :disabled state as for the normal state (well, except for the cursor, which realistically, isn’t going to produce different results save for exceptional cases anyway). What gives, Firefox?!

Comparison of styles set in Firefox for <input type='color'> in its normal state and its :disabled state. The padding and border set in the :disabled case are exactly the same as those set in the normal case.”/><figcaption>Firefox <code>:disabled</code> (top) versus normal (bottom) styling.</figcaption></figure>
<p>In Edge, both the <code>border-color</code> and the <code>background</code> gradient are different.</p>
<figure><img src=
Edge :disabled styling (by checking computed styles).

We have the following styles for the normal state:

border-color: rgb(112, 112, 112); background-image: linear-gradient(rgb(236, 236, 236), rgb(213, 213, 213));

And for the :disabled state:

border-color: rgb(186, 186, 186); background-image: linear-gradient(rgb(237, 237, 237), rgb(229, 229, 229));

Clearly different if we look at the code and visually better than Chrome, though it still may not be quite enough:

Disabled and enabled input side by side in Edge. There is a slight difference in background-image and a bigger difference in border-color, but it still may be difficult to tell whether an input is enabled or not at first sight without having a reference to compare.
Disabled (left) versus enabled (right) <input type='color'> in Edge.
:focus

This is one state we can test by toggling the DevTools pseudo-classes. Well, in theory. In practice, it doesn’t really help us in all browsers.

Starting with Chrome, we can see that we have an outline in this state and the outline-color computes to rgb(77, 144, 254), which is some kind of blue.

Chrome DevTools screenshot showing an outline for an input having <code>:focus</code>.”/><figcaption>Chrome <code>:focus</code> styling.</figcaption></figure>
<p>Pretty straightforward and easy to spot.</p>
<p>Moving on to Firefox, things start to get hairy! Unlike Chrome, toggling the <code>:focus</code> pseudo-class from DevTools does nothing on the input element, though by focusing it (by tab click), the <code>border</code> becomes blue and we get a <code>dotted</code> rectangle within — but there’s no indication in DevTools regarding what is happening.</p>
<figure><img src=
What happens in Firefox when tabbing to our input to :focus it.

If we check Firefox’s forms.css, it provides an explanation for the dotted rectangle. This is the dotted border of a pseudo-element, ::-moz-focus-inner (a pseudo-element which, for some reason, isn’t shown in DevTools inside our input as ::-moz-color-swatch is). This border is initially transparent and then becomes visible when the input is focused — the pseudo-class used here (:-moz-focusring) is pretty much an old Firefox version of the new standard (:focus-visible), which is currently only supported by Chrome behind the Experimental Web Platform features flag.

Firefox DevTools screenshot where the inner dotted rectangle on :focus comes from: it is set as a transparent border on the ::-moz-focus-inner pseudo-element and it becomes visible when the input should have a noticeable :focus indicator.
Firefox: where the inner dotted rectangle on :focus comes from.

What about the blue border? Well, it appears this one isn’t set by a stylesheet, but at an OS level instead. The good news is we can override all these styles should we choose to do so.

In Edge, we’re faced with a similar situation. Nothing happens when toggling the :focus pseudo-class from DevTools, but if we actually tab to our input to focus it, we can see an inner dotted rectangle.

Animated gif. Shows how, on :focus, our input gets an inner dotted rectangle.
What happens in Edge when tabbing to our input to :focus it.

Even though I have no way of knowing for sure, I suspect that, just like in Firefox, this inner rectangle is due to a pseudo-element that becomes visible on :focus.

:hover

In Chrome, toggling this pseudo-class doesn’t reveal any :hover-specific styles in DevTools. Furthermore, actually hovering the input doesn’t appear to change anything visually. So it looks like Chrome really doesn’t have any :hover-specific styles?

In Firefox, toggling the :hover pseudo-class from DevTools reveals a new rule in the styles panel:

Screenshot of Firefox DevTools showing the rule set that shows up for the :hover state.
Firefox :hover styling as seen in DevTools.

When actually hovering the input, we see the background turns light blue and the border blue, so the first thought would be that light blue is the -moz-buttonhoverface value and that the blue border is again set at an OS level, just like in the :focus case.

Animated gif. Shows that, on actually hovering our <input type='color'>, it gets a light blue background and a blue border.”/><figcaption>What actually happens in Firefox on <code>:hover</code>.</figcaption></figure>
<p>However, if we look at the computed styles, we see the same <code>background</code> we have in the normal state, so that blue <code>background</code> is probably really set at an OS level as well, in spite of having that rule in the <code>forms.css</code> stylesheet.</p>
<figure><img src=
Firefox: computed background-color of an <input type='color'> on :hover.

In Edge, toggling the :hover pseudo-class from DevTools gives our input a light blue (rgb(166, 244, 255)) background and a blue (rgb(38, 160, 218)) border, whose exact values we can find in the Computed tab:

Screenshot of Edge DevTools showing the computed value for background-color and border-color in the :hover state.
Edge: computed background-color and border-color of an <input type='color'> on :hover.
:active

Checking the :active state in the Chrome DevTools does nothing visually and shows no specific rules in the Styles panel. However, if we actually click our input, we see that the background gradient that doesn’t even show up in DevTools in the normal state gets reversed.

Screenshot of the input in :active state in Chrome. A very light, almost white, grey to another light, but still darker grey gradient from bottom to top can be seen as the background, not the solid background-color indicated by DevTools.
What the actual input looks like in Chrome in the :active state. It appears to have a gradient (reversed from the normal state), in spite of the info we get from DevTools telling us it doesn’t.

In Firefox DevTools, toggling the :active state on does nothing, but if we also toggle the :hover state on, then we get a rule set that changes the inline padding (the block padding is set to the same value of 0 it has in all other states), the border-style and sets the background-color back to our old friend ButtonFace.

Screenshot of Firefox DevTools showing the rule set that shows up for the :active state.
Firefox :active styling as seen in DevTools.

In practice, however, the only thing that matches the info we get from DevTools is the inline shift given by the change in logical padding. The background becomes a lighter blue than the :hover state and the border is blue. Both of these changes are probably happening at an OS level as well.

Animated gif. Shows that, on actually clicking our <input type='color'>, it gets a light blue background and a blue border in addition to sliding 1 pixel in the inline direction as a result of changing the inline padding.”/><figcaption>What actually happens in Firefox in an <code>:active</code> state.</figcaption></figure>
<p>In Edge, activating the <code>:active</code> class from DevTools gives us the exact same styles we have for the <code>:hover</code> state. However, if we have both the <code>:hover</code> and the <code>:active</code> states on, things change a bit. We still have a light blue <code>background</code> and a blue <code>border</code>, but both are darker now (<code>rgb(52, 180, 227)</code> for the <code>background-color</code> and <code>rgb(0, 137, 180)</code> for the <code>border-color</code>):</p>
<figure><img src=
The computed background-color and border-color of an <input type='color'> on :active viewed in Edge.

This is the takeaway: if we want a consistent cross-browser results for <input type='color'>, we should define our own clearly distinguishable styles for all these states ourselves because, fortunately, almost all the browser defaults — except for the inner rectangle we get in Edge on :focus — can be overridden.

The swatch wrapper

This is a component we only see in Chrome, so if we want a cross-browser result, we should probably ensure it doesn’t affect the swatch inside — this means ensuring it has no margin, border, padding or background and that its dimensions equal those of the actual input’s content-box.

In order to know whether we need to mess with these properties (and maybe others as a result) or not, let’s see what the browser defaults are for them.

Fortunately, we have no margin or border, so we don’t need to worry about these.

Chrome DevTools screenshot showing the margin and border values for the swatch wrapper.
The margin and border values for the swatch wrapper in Chrome.

We do however have a non-zero padding (of 4px 2px), so this is something we’ll need to zero out if we want to achieve a consistent cross-browser result.

Chrome DevTools screenshot showing the padding values for the swatch wrapper.
The padding values for the swatch wrapper in Chrome.

The dimensions are both conveniently set to 100%, which means we won’t need to mess with them.

Chrome DevTools screenshot showing the size values for the swatch wrapper.
The size values for the swatch wrapper in Chrome.

Something we need to note here is that we have box-sizing set to border-box, so the padding gets subtracted from the dimensions set on this wrapper.

Chrome DevTools screenshot showing the <code>box-sizing</code> value for the swatch wrapper.”/><figcaption>The <code>box-sizing</code> value for the swatch wrapper in Chrome.</figcaption></figure>
<p>This means that while the <code>padding-box</code>, <code>border-box</code> and <code>margin-box</code> of our wrapper (all equal because we have no <code>margin</code> or <code>border</code>) are identical to the <code>content-box</code> of the actual <code><input type='color'></code> (which is <code>44px</code>x<code>23px</code> in Chrome), getting the wrapper’s <code>content-box</code> involves subtracting the <code>padding</code> from these dimensions. It results that this box is <code>40px</code>x<code>15px</code>.</p>
<figure><img src=
The box model for the swatch wrapper in Chrome.

The background is set to transparent, so that’s another property we don’t need to worry about resetting.

Chrome DevTools screenshot showing the background values for the swatch wrapper.
The background values for the swatch wrapper in Chrome.

There’s one more property set on this element that caught my attention: display. It has a value of flex, which means its children are flex items.

Chrome DevTools screenshot showing the display value for the swatch wrapper.
The display value for the swatch wrapper in Chrome.

The swatch

This is a component we can style in Chrome and Firefox. Sadly, Edge doesn’t expose it to allow us to style it, so we cannot change properties we might want to, such as border, border-radius or box-shadow.

The box-sizing property is one we need to set explicitly if we plan on giving the swatch a border or a padding because its value is content-box in Chrome, but border-box in Firefox.

Comparative screenshots of DevTools in the two browsers showing the computed values of box-sizing for the swatch component.
The box-sizing values for the swatch viewed in Chrome (top) and Firefox (bottom).

Fortunately, the font-size is inherited from the input itself so it’s the same.

Comparative screenshots of DevTools in the two browsers showing the computed values of font-size for the swatch component.
The font-size values for the swatch viewed in Chrome (top) and Firefox (bottom).

The margin computes to 0 in both Chrome and Firefox.

Comparative screenshots of DevTools in the two browsers showing the computed values of margin for the swatch component.
The margin values for the swatch viewed in Chrome (top) and Firefox (bottom).

This is because most margins haven’t been set, so they end up being 0 which is the default for <div> elements. However, Firefox is setting the inline margins to auto and we’ll be getting to why that computes to 0 in just a little moment.

Screenshot of Firefox DevTools.
The inline margin for the swatch being set to auto in Firefox.

The border is solid 1px in both browsers. The only thing that differs is the border-color, which is rgb(119, 119, 119) in Chrome and grey (or rgb(128, 128, 128), so slightly lighter) in Firefox.

Comparative screenshots of DevTools in the two browsers showing the computed values of border for the swatch component.
The border values for the swatch viewed in Chrome (top) and Firefox (bottom).

Note that the computed border-width in Firefox (at least on Windows) depends on the OS zoom level, just as it is in the case of the actual input.

The padding is luckily 0 in both Chrome and Firefox.

Comparative screenshots of DevTools in the two browsers showing the computed values of padding for the swatch component.
The padding values for the swatch viewed in Chrome (top) and Firefox (bottom).

The dimensions end up being exactly what we’d expect to find, assuming the swatch covers its parent’s entire content-box.

Comparative screenshots of DevTools in the two browsers showing the box model for the swatch component.
The box model for the swatch viewed in Chrome (top) and Firefox (bottom).

In Chrome, the swatch parent is the <div> wrapper we saw earlier, whose content-box is 4pxx15px. This is equal to the margin-box and the border-box of the swatch (which coincide as we have no margin). Since the padding is 0, the content-box and the padding-box for the swatch are identical and, subtracting the 1px border, we get dimensions that are 38pxx13px.

In Firefox, the swatch parent is the actual input, whose content-box is 44pxx19px one. This is equal to the margin-box and the border-box of the swatch (which coincide as we have no margin). Since the padding is 0, the content-box and the padding-box for the swatch are identical and, subtracting the 1px border, we get that their dimensions are 42pxx17px.

In Firefox, we see that the swatch is made to cover its parent’s content-box by having both its dimensions set to 100%.

Comparative screenshots of DevTools in the two browsers showing the size values for the swatch component.
The size values for the swatch viewed in Chrome (top) and Firefox (bottom).

This is the reason why the auto value for the inline margin computes to 0.

But what about Chrome? We cannot see any actual dimensions being set. Well, this result is due to the flex layout and the fact that the swatch is a flex item that’s made to stretch such that it covers its parent’s content-box.

Chrome DevTools screenshot showing the flex value for the swatch wrapper.
The flex value for the swatch wrapper in Chrome.

Final thoughts

Phew, we covered a lot of ground here! While it may seem exhaustive to dig this deep into one specific element, this is the sort of exercise that illustrates how difficult cross-browser support can be. We have our own styles, user agent styles and operating system styles to traverse and some of those are always going to be what they are. But, as we discussed at the very top, this winds up being an accessibility issue at the end of the day, and something to really consider when it comes to implementing a practical, functional application of a color input.

Remember, a lot of this is ripe territory to reach out to browser vendors and let them know how they can update their implementations based on your reported use cases. Here are the three tickets I mentioned earlier where you can either chime in or reference to create a new ticket:

The post Color Inputs: A Deep Dive into Cross-Browser Differences appeared first on CSS-Tricks.

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A Deep Dive into Native Lazy-Loading for Images and Frames

Today’s websites are packed with heavy media assets like images and videos. Images make up around 50% of an average website’s traffic. Many of them, however, are never shown to a user because they’re placed way below the fold.

What’s this thing about images being lazy, you ask? Lazy-loading is something that’s been covered quite a bit here on CSS-Tricks, including a thorough guide with documentation for different approaches using JavaScript. In short, we’re talking about a mechanism that defers the network traffic necessary to load content when it’s needed — or rather when trigger the load when the content enters the viewport.

The benefit? A smaller initial page that loads faster and saves network requests for items that may not be needed if the user never gets there.

If you read through other lazy-loading guides on this or other sites, you’ll see that we’ve had to resort to different tactics to make lazy-loading work. Well, that’s about to change when lazy-loading will be available natively in HTML as a new loading attribute… at least in Chrome which will hopefully lead to wider adoption. Chrome has already merged the code for native lazy-loading and is expected to ship it in Chrome 75, which is slated to release June 4, 2019.

Eager cat loaded lazily (but still immediately because it's above the fold)

The pre-native approach

Until now, developers like ourselves have had to use JavaScript (whether it’s a library or something written from scratch) in order to achieve lazy-loading. Most libraries work like this:

  • The initial, server-side HTML response includes an img element without the src attribute so the browser does not load any data. Instead, the image’s URL is set as another attribute in the element’s data set, e. g. data-src.
  • <img data-src="https://tiny.pictures/example1.jpg" alt="...">
  • Then, a lazy-loading library is loaded and executed.
  • <script src="LazyLoadingLibrary.js"></script> <script>LazyLoadingLibrary.run()</script>
  • That keeps track of the user’s scrolling behavior and tells the browser to load the image when it is about to be scrolled into view. It does that by copying the data-src attribute’s value to the previously empty src attribute.
  • <img src="https://tiny.pictures/example1.jpg" data-src="https://tiny.pictures/example1.jpg" alt="...">

This has worked for a pretty long time now and gets the job done. But it’s not ideal for good reasons.

The obvious problem with this approach is the length of the critical path for displaying the website. It consists of three steps, which have to be carried out in sequence (after each other):

  1. Load the initial HTML response
  2. Load the lazy-loading library
  3. Load the image file

If this technique is used for images above the fold the website will flicker during loading because it is first painted without the image (after step 1 or 2, depending on if the script uses defer or async) and then — after having been loaded — include the image. It will also be perceived as loading slowly.

In addition, the lazy-loading library itself puts an extra weight on the website’s bandwidth and CPU requirements. And let’s not forget that a JavaScript approach won’t work for people who have JavaScript disabled (although we shouldn’t really care about them in 2019, should we?).

Oh, and what about sites that rely on RSS to distribute content, like CSS-Tricks? The initial image-less render means there are no images in the RSS version of content as well.

And so on.

Native lazy-loading to the rescue!

Lazy cat loaded lazily

As we noted at the start, Chromium and Google Chrome will ship a native lazy-loading mechanism in the form of a new loading attribute, starting in Chrome 75. We’ll go over the attribute and its values in just a bit, but let’s first get it working in our browsers so we can check it out together.

Enable native lazy-loading

Until Chrome 75 is officially released, we have Chrome Canary and can enable lazy-loading manually by switching two flags.

  1. Open chrome://flags in Chromium or Chrome Canary.
  2. Search for lazy.
  3. Enable both the “Enable lazy image loading” and the “Enable lazy frame loading” flag.
  4. Restart the browser with the button in the lower right corner of the screen.
Native lazy-loading flags in Google Chrome

You can check if the feature is properly enabled by opening your JavaScript console (F12). You should see the following warning:

[Intervention] Images loaded lazily and replaced with placeholders. Load events are deferred.”

All set? Now we get to dig into the loading attribute.

The loading attribute

Both the img and the iframe elements will accept the loading attribute. It’s important to note that its values will not be taken as a strict order by the browser but rather as a hint to help the browser make its own decision whether or not to load the image or frame lazily.

The attribute can have three values which are explained below. Next to the images, you’ll find tables listing your individual resource loading timings for this page load. Range response refers to a kind of partial pre-flight request made to determine the image’s dimensions (see How it works) for details). If this column is filled, the browser made a successful range request.

Please note the startTime column, which states the time image loading was deferred after the DOM had been parsed. You might have to perform a hard reload (CTRL + Shift + R) to re-trigger range requests.

The auto (or unset) value

<img src="auto-cat.jpg" loading="auto" alt="..."> <img src="auto-cat.jpg" alt="..."> <iframe src="https://css-tricks.com/" loading="auto"></iframe> <iframe src="https://css-tricks.com/"></iframe>
Auto cat loaded automatically
Auto cat loaded automatically

Setting the loading attribute to auto (or simply leaving the value blank, as in loading="") lets the browser decide whether or not to lazy-load an image. It takes many things into consideration to make that decision, like the platform, whether Data Saver mode is enabled, network conditions, image size, image vs. iframe, the CSS display property, among others. (See How it works) for info about why all this is important.)

The eager value

<img src="auto-cat.jpg" loading="eager" alt="..."> <iframe src="https://css-tricks.com/" loading="eager"></iframe>
Eager cat loaded eagerly
Eager cat loaded eagerly

The eager value provides a hint to the browser that an image should be loaded immediately. If loading was already deferred (e. g. because it had been set to lazy and was then changed to eager by JavaScript), the browser should start loading the image immediately.

The lazy value

<img src="auto-cat.jpg" loading="lazy" alt="..."> <iframe src="https://css-tricks.com/" loading="lazy"></iframe>
Lazy cat loaded lazily
Lazy cat loaded lazily

The lazy value provides a hints to the browser that an image should be lazy-loaded. It’s up to the browser to interpret what exactly this means, but the explainer document states that it should start loading when the user scrolls “near” the image such that it is probably loaded once it actually comes into view.

How the loading attribute works

In contrast to JavaScript lazy-loading libraries, native lazy-loading uses a kind of pre-flight request to get the first 2048 bytes of the image file. Using these, the browser tries to determine the image’s dimensions in order to insert an invisible placeholder for the full image and prevent content from jumping during loading.

The image’s load event is fired as soon as the full image is loaded, be it after the first request (for images smaller than 2 KB) or after the second one. Please note that the load event may never be fired for certain images because the second request is never made.

In the future, browsers might make twice as many image requests as there would be under the current proposal. First the range request, then the full request. Make sure your servers support the HTTP Range: 0-2047 header and respond with status code 206 (Partial Content) to prevent them from delivering the full image twice.

Due to the higher number of subsequent requests made by the same user, web server support for the HTTP/2 protocol will become more important.

Let’s talk about deferred content. Chrome’s rendering engine Blink uses heuristics to determine which content should be deferred and for how long to defer it. You can find a comprehensive list of requirements in Scott Little’s design documentation. This is a short breakdown of what will be deferred:

  • Images and frames on all platforms which have loading="lazy" set
  • Images on Chrome for Android with Data Saver enabled and that satisfy all of the following:
    • loading="auto" or unset
    • no width and height attributes smaller than 10px
    • not created programmatically in JavaScript
  • Frames which satisfy all of the following:
    • loading="auto" or unset
    • is from a third-party (different domain or protocol than the embedding page)
    • larger than 4 pixels in height and width (to prevent deferring tiny tracking frames)
    • not marked as display: none or visibility: hidden (again, to prevent deferring tracking frames)
    • not positioned off-screen using negative x or y coordinates

Responsive images with srcset

Native lazy-loading also works with responsive img elements using the srcset attribute. This attribute offers a list of image file candidates to the browser. Based on the user’s screen size, display pixel ratio, network conditions, etc., the browser will choose the optimal image candidate for the occasion. Image optimization CDNs like tiny.pictures are able to provide all image candidates in real-time without any back end development necessary.

<img src="https://demo.tiny.pictures/native-lazy-loading/lazy-cat.jpg" srcset="https://demo.tiny.pictures/native-lazy-loading/lazy-cat.jpg?width=400 400w, https://demo.tiny.pictures/native-lazy-loading/lazy-cat.jpg?width=800 800w" loading="lazy" alt="...">

Browser support

At the time of this writing, no browser supports native-loading by default. However, Chrome will enable the feature, as we’ve covered, starting in Chrome 75. No other browser vendor has announced support so far. (Edge being a kind of exception because it will soon make the switch to Chromium.)

You can detect the feature with a few lines of JavaScript:

if ("loading" in HTMLImageElement.prototype) {   // Support. } else {   // No support. You might want to dynamically import a lazy-loading library here (see below). }

See the Pen
Native lazy-loading browser support
by Erk Struwe (@erkstruwe)
on CodePen.

Automatic fallback to JavaScript solution with low-quality image placeholder

One very cool feature of most JavaScript-based lazy-loading libraries is the low-quality image placeholder (LQIP). Basically, it leverages the idea that browsers load (or perhaps I should say used to load) the src of an img element immediately, even if it gets later replaced by another URL. This way, it’s possible to load a tiny file size, low-quality image file on page load and later replace it with a full-sized version.

We can now use this to mimic the native lazy-loading’s 2 KB range requests in browsers that do not support this feature in order to achieve the same result, namely a placeholder with the actual image dimensions and a tiny file size.

See the Pen
Native lazy-loading with JavaScript library fallback and low-quality image placeholder
by Erk Struwe (@erkstruwe)
on CodePen.

Conclusion

I’m really excited about this feature. And frankly, I’m still wondering why it hasn’t got much more attention until now, given the fact that its release is imminent and the impact on global internet traffic will be remarkable, even if only small parts of the heuristics are changed.

Think about it: After a gradual roll-out for the different Chrome platforms and with auto being the default setting, the world’s most popular browser will soon lazy-load below-the-fold images and frames by default. Not only will the traffic amount of many badly-written websites drop significantly, but web servers will be hammered with tiny requests for image dimension detection.

And then there’s tracking: Assuming many unsuspecting tracking pixels and frames will be prevented from being loaded, the analytics and affiliate industry will have to act. We can only hope they don’t panic and add loading="eager" to every single image, rendering this great feature useless for their users. They should rather change their code to be recognized as tracking pixels by the heuristics described above.

Web developers, analytics and operations managers should check their website’s behavior with this feature and their servers’ support for Range requests and HTTP/2 immediately.

Image optimization CDNs could help out in case there are any issues to be expected or if you’d like to take image delivery optimization to the max (including automatic WebP support, low-quality image placeholders, and much more). Read more about tiny.pictures!

References

The post A Deep Dive into Native Lazy-Loading for Images and Frames appeared first on CSS-Tricks.

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