Month: May 2020

Increment Issue 13: Frontend

Increment is a beautiful quarterly magazine (print and web) published by Stripe “about how teams build and operate software systems at scale”. While there is always stuff about making websites in general, this issue is the first focused on front-end¹ development.

I’ve got an article in there: When frontend means full stack. I’ll probably someday port it over here and perhaps add some more context (there were some constraints for print) but I love how it turned out on their site! A taste:

We handle this growing responsibility in different ways. Even though we all technically fall within the same big-tent title, many frontend developers wind up specializing. Often, we don’t have a choice. The term “unicorn” once described the extremely rare person who was good at both frontend and backend development, but these days it’s just as rare to find people skilled at the full spectrum of frontend development. In fact, the term “full stack” has largely come to mean “a frontend developer who does a good amount of the stuff a backend developer used to do.”

The whole issue is chock full of wonderful authors:

And the article that is the most right up my alley, Why is CSS . . . the way it is? by Chris Lilley. It’s somehow astonishing, gutwrenching, understandable, and comfortable to know that CSS evolves like any other software project. Sometimes thoughtfully and carefully, and sometimes with a meh, we’ll fix it later.

Once a feature is in place, it’s easier to slightly improve it than to add a new, better, but completely different feature that does the same thing.

This explains, for example, why list markers were initially specified in CSS by expanding the role of float. (The list marker was floated left so the list item text wrapped around it to the right.) That effort was abandoned and replaced by the list-style-position property, whose definition currently has the following, not very confidence-inspiring inline issue: “This is handwavey nonsense from CSS2, and needs a real definition.”

That’s a damn fine collection of writings on front end if you ask me.

A big thank you to Sid Orlando and Molly McArdle who helped me through the process and seem to do a great job running the ship over there.

  1. The issue uses “frontend” throughout, and I appreciate them having a styleguide and being consistent about it. But I can’t bring myself to use it. 🔗 The term “front-end” is correct when used as a compound adjective, and the term “front end” is correct when used as a noun.

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Global CSS options with custom properties

With a preprocessor, like Sass, building a logical “do this or don’t” setting is fairly straightforward:

$  option: false;  @mixin doThing {   @if $  option {     do-thing: yep;   } }  .el {   @include doThing; }

Can we do that in native CSS with custom properties? Mark Otto shows that we can. It’s just a smidge different.

html {   --component-shadow: 0 .5rem 1rem rgba(0,0,0,.1); }  .component {   box-shadow: var(--component-shadow); }  <!-- override the global anywhere more specific! like      <div class="component remove-shadow">      or      <body class="remove-shadow"> --> .remove-shadow {   --component-shadow: none; }

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5 Good Reasons to Switch for the Brave Browser


Jamstack News!

I totally forgot that the Jamstack Conf was this week but thankfully they’ve already published the talks on the Jamstack YouTube channel. I’m really looking forward to sitting down with these over a coffee while I also check out Netlify’s other big release today: Build Plugins.

These are plugins that run whenever your site is building. One example is the A11y plugin that will fail a build if accessibility failures are detected. Another minifies HTML and there’s even one that inlines critical CSS. What’s exciting is that these build plugins are kinda making complex Gulp/Grunt environments the stuff of legend. Instead of going through the hassle of config stuff, build plugins let Netlify figure it all out for you. And that’s pretty neat.

Also, our very own Sarah Drasner wrote just about how to create your first Netlify Build Plugin. So, if you have an idea for something that you could share with the community, then that may be the best place to start.

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Building Your First Serverless Service With AWS Lambda Functions

Many developers are at least marginally familiar with AWS Lambda functions. They’re reasonably straightforward to set up, but the vast AWS landscape can make it hard to see the big picture. With so many different pieces it can be daunting, and frustratingly hard to see how they fit seamlessly into a normal web application.

The Serverless framework is a huge help here. It streamlines the creation, deployment, and most significantly, the integration of Lambda functions into a web app. To be clear, it does much, much more than that, but these are the pieces I’ll be focusing on. Hopefully, this post strikes your interest and encourages you to check out the many other things Serverless supports. If you’re completely new to Lambda you might first want to check out this AWS intro.

There’s no way I can cover the initial installation and setup better than the quick start guide, so start there to get up and running. Assuming you already have an AWS account, you might be up and running in 5–10 minutes; and if you don’t, the guide covers that as well.

Your first Serverless service

Before we get to cool things like file uploads and S3 buckets, let’s create a basic Lambda function, connect it to an HTTP endpoint, and call it from an existing web app. The Lambda won’t do anything useful or interesting, but this will give us a nice opportunity to see how pleasant it is to work with Serverless.

First, let’s create our service. Open any new, or existing web app you might have (create-react-app is a great way to quickly spin up a new one) and find a place to create our services. For me, it’s my lambda folder. Whatever directory you choose, cd into it from terminal and run the following command:

sls create -t aws-nodejs --path hello-world

That creates a new directory called hello-world. Let’s crack it open and see what’s in there.

If you look in handler.js, you should see an async function that returns a message. We could hit sls deploy in our terminal right now, and deploy that Lambda function, which could then be invoked. But before we do that, let’s make it callable over the web.

Working with AWS manually, we’d normally need to go into the AWS API Gateway, create an endpoint, then create a stage, and tell it to proxy to our Lambda. With serverless, all we need is a little bit of config.

Still in the hello-world directory? Open the serverless.yaml file that was created in there.

The config file actually comes with boilerplate for the most common setups. Let’s uncomment the http entries, and add a more sensible path. Something like this:

functions:   hello:     handler: handler.hello #   The following are a few example events you can configure #   NOTE: Please make sure to change your handler code to work with those events #   Check the event documentation for details     events:       - http:         path: msg         method: get

That’s it. Serverless does all the grunt work described above.

CORS configuration 

Ideally, we want to call this from front-end JavaScript code with the Fetch API, but that unfortunately means we need CORS to be configured. This section will walk you through that.

Below the configuration above, add cors: true, like this

functions:   hello:     handler: handler.hello     events:       - http:         path: msg         method: get         cors: true

That’s the section! CORS is now configured on our API endpoint, allowing cross-origin communication.

CORS Lambda tweak

While our HTTP endpoint is configured for CORS, it’s up to our Lambda to return the right headers. That’s just how CORS works. Let’s automate that by heading back into handler.js, and adding this function:

const CorsResponse = obj => ({   statusCode: 200,   headers: {     "Access-Control-Allow-Origin": "*",     "Access-Control-Allow-Headers": "*",     "Access-Control-Allow-Methods": "*"   },   body: JSON.stringify(obj) });

Before returning from the Lambda, we’ll send the return value through that function. Here’s the entirety of handler.js with everything we’ve done up to this point:

'use strict'; const CorsResponse = obj => ({   statusCode: 200,   headers: {     "Access-Control-Allow-Origin": "*",     "Access-Control-Allow-Headers": "*",     "Access-Control-Allow-Methods": "*"   },   body: JSON.stringify(obj) }); 
 module.exports.hello = async event => {   return CorsResponse("HELLO, WORLD!"); };

Let’s run it. Type sls deploy into your terminal from the hello-world folder.

When that runs, we’ll have deployed our Lambda function to an HTTP endpoint that we can call via Fetch. But… where is it? We could crack open our AWS console, find the gateway API that serverless created for us, then find the Invoke URL. It would look something like this.

The AWS console showing the Settings tab which includes Cache Settings. Above that is a blue notice that contains the invoke URL.

Fortunately, there is an easier way, which is to type sls info into our terminal:

Just like that, we can see that our Lambda function is available at the following path:

Woot, now let’s call It!

Now let’s open up a web app and try fetching it. Here’s what our Fetch will look like:

fetch("")   .then(resp => resp.json())   .then(resp => {     console.log(resp);   });

We should see our message in the dev console.

Console output showing Hello World.

Now that we’ve gotten our feet wet, let’s repeat this process. This time, though, let’s make a more interesting, useful service. Specifically, let’s make the canonical “resize an image” Lambda, but instead of being triggered by a new S3 bucket upload, let’s let the user upload an image directly to our Lambda. That’ll remove the need to bundle any kind of aws-sdk resources in our client-side bundle.

Building a useful Lambda

OK, from the start! This particular Lambda will take an image, resize it, then upload it to an S3 bucket. First, let’s create a new service. I’m calling it cover-art but it could certainly be anything else.

sls create -t aws-nodejs --path cover-art

As before, we’ll add a path to our HTTP endpoint (which in this case will be a POST, instead of GET, since we’re sending the file instead of receiving it) and enable CORS:

// Same as before   events:     - http:       path: upload       method: post       cors: true

Next, let’s grant our Lambda access to whatever S3 buckets we’re going to use for the upload. Look in your YAML file — there should be a iamRoleStatements section that contains boilerplate code that’s been commented out. We can leverage some of that by uncommenting it. Here’s the config we’ll use to enable the S3 buckets we want:

iamRoleStatements:  - Effect: "Allow"    Action:      - "s3:*"    Resource: ["arn:aws:s3:::your-bucket-name/*"]

Note the /* on the end. We don’t list specific bucket names in isolation, but rather paths to resources; in this case, that’s any resources that happen to exist inside your-bucket-name.

Since we want to upload files directly to our Lambda, we need to make one more tweak. Specifically, we need to configure the API endpoint to accept multipart/form-data as a binary media type. Locate the provider section in the YAML file:

provider:   name: aws   runtime: nodejs12.x

…and modify if it to:

provider:   name: aws   runtime: nodejs12.x   apiGateway:     binaryMediaTypes:       - 'multipart/form-data'

For good measure, let’s give our function an intelligent name. Replace handler: handler.hello with handler: handler.upload, then change module.exports.hello to module.exports.upload in handler.js.

Now we get to write some code

First, let’s grab some helpers.

npm i jimp uuid lambda-multipart-parser

Wait, what’s Jimp? It’s the library I’m using to resize uploaded images. uuid will be for creating new, unique file names of the sized resources, before uploading to S3. Oh, and lambda-multipart-parser? That’s for parsing the file info inside our Lambda.

Next, let’s make a convenience helper for S3 uploading:

const uploadToS3 = (fileName, body) => {   const s3 = new S3({});   const  params = { Bucket: "your-bucket-name", Key: `/$ {fileName}`, Body: body }; 
   return new Promise(res => {     s3.upload(params, function(err, data) {       if (err) {         return res(CorsResponse({ error: true, message: err }));       }       res(CorsResponse({          success: true,          url: `https://$ {params.Bucket}$ {params.Key}`        }));     });   }); };

Lastly, we’ll plug in some code that reads the upload files, resizes them with Jimp (if needed) and uploads the result to S3. The final result is below.

'use strict'; const AWS = require("aws-sdk"); const { S3 } = AWS; const path = require("path"); const Jimp = require("jimp"); const uuid = require("uuid/v4"); const awsMultiPartParser = require("lambda-multipart-parser"); 
 const CorsResponse = obj => ({   statusCode: 200,   headers: {     "Access-Control-Allow-Origin": "*",     "Access-Control-Allow-Headers": "*",     "Access-Control-Allow-Methods": "*"   },   body: JSON.stringify(obj) }); 
 const uploadToS3 = (fileName, body) => {   const s3 = new S3({});   var params = { Bucket: "your-bucket-name", Key: `/$ {fileName}`, Body: body };   return new Promise(res => {     s3.upload(params, function(err, data) {       if (err) {         return res(CorsResponse({ error: true, message: err }));       }       res(CorsResponse({          success: true,          url: `https://$ {params.Bucket}$ {params.Key}`        }));     });   }); }; 
 module.exports.upload = async event => {   const formPayload = await awsMultiPartParser.parse(event);   const MAX_WIDTH = 50;   return new Promise(res => {[0].content, function(err, image) {       if (err || !image) {         return res(CorsResponse({ error: true, message: err }));       }       const newName = `$ {uuid()}$ {path.extname(formPayload.files[0].filename)}`;       if (image.bitmap.width > MAX_WIDTH) {         image.resize(MAX_WIDTH, Jimp.AUTO);         image.getBuffer(image.getMIME(), (err, body) => {           if (err) {             return res(CorsResponse({ error: true, message: err }));           }           return res(uploadToS3(newName, body));         });       } else {         image.getBuffer(image.getMIME(), (err, body) => {           if (err) {             return res(CorsResponse({ error: true, message: err }));           }           return res(uploadToS3(newName, body));         });       }     });   }); };

I’m sorry to dump so much code on you but — this being a post about Amazon Lambda and serverless — I’d rather not belabor the grunt work within the serverless function. Of course, yours might look completely different if you’re using an image library other than Jimp.

Let’s run it by uploading a file from our client. I’m using the react-dropzone library, so my JSX looks like this:

<Dropzone   onDrop={files => onDrop(files)}   multiple={false} >   <div>Click or drag to upload a new cover</div> </Dropzone>

The onDrop function looks like this:

const onDrop = files => {   let request = new FormData();   request.append("fileUploaded", files[0]); 
   fetch("", {     method: "POST",     mode: "cors",     body: request     })   .then(resp => resp.json())   .then(res => {     if (res.error) {       // handle errors     } else {       // success - woo hoo - update state as needed     }   }); };

And just like that, we can upload a file and see it appear in our S3 bucket! 

Screenshot of the AWS interface for buckets showing an uploaded file in a bucket that came from the Lambda function.

An optional detour: bundling

There’s one optional enhancement we could make to our setup. Right now, when we deploy our service, Serverless is zipping up the entire services folder and sending all of it to our Lambda. The content currently weighs in at 10MB, since all of our node_modules are getting dragged along for the ride. We can use a bundler to drastically reduce that size. Not only that, but a bundler will cut deploy time, data usage, cold start performance, etc. In other words, it’s a nice thing to have.

Fortunately for us, there’s a plugin that easily integrates webpack into the serverless build process. Let’s install it with:

npm i serverless-webpack --save-dev

…and add it via our YAML config file. We can drop this in at the very end:

// Same as before plugins:   - serverless-webpack

Naturally, we need a webpack.config.js file, so let’s add that to the mix:

const path = require("path"); module.exports = {   entry: "./handler.js",   output: {     libraryTarget: 'commonjs2',     path: path.join(__dirname, '.webpack'),     filename: 'handler.js',   },   target: "node",   mode: "production",   externals: ["aws-sdk"],   resolve: {     mainFields: ["main"]   } };

Notice that we’re setting target: node so Node-specific assets are treated properly. Also note that you may need to set the output filename to  handler.js. I’m also adding aws-sdk to the externals array so webpack doesn’t bundle it at all; instead, it’ll leave the call to const AWS = require("aws-sdk"); alone, allowing it to be handled by our Lamdba, at runtime. This is OK since Lambdas already have the aws-sdk available implicitly, meaning there’s no need for us to send it over the wire. Finally, the mainFields: ["main"] is to tell webpack to ignore any ESM module fields. This is necessary to fix some issues with the Jimp library.

Now let’s re-deploy, and hopefully we’ll see webpack running.

Now our code is bundled nicely into a single file that’s 935K, which zips down further to a mere 337K. That’s a lot of savings!

Odds and ends

If you’re wondering how you’d send other data to the Lambda, you’d add what you want to the request object, of type FormData, from before. For example:

request.append("xyz", "Hi there");

…and then read in the Lambda. This can be useful if you need to send a security token, or other file info.

If you’re wondering how you might configure env variables for your Lambda, you might have guessed by now that it’s as simple as adding some fields to your serverless.yaml file. It even supports reading the values from an external file (presumably not committed to git). This blog post by Philipp Müns covers it well.

Wrapping up

Serverless is an incredible framework. I promise, we’ve barely scratched the surface. Hopefully this post has shown you its potential, and motivated you to check it out even further.

If you’re interested in learning more, I’d recommend the learning materials from David Wells, an engineer at Netlify, and former member of the serverless team, as well as the Serverless Handbook by Swizec Teller

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Too funny:

After careful consideration, we settled on rearchitecting our platform to use $ FLASHY_LANGUAGE and $ HYPED_TECHNOLOGY. Not only is $ FLASHY_LANGUAGE popular according to the Stack Overflow developer survey, it’s also cross platform; we’re using it to reimplement our mobile apps as well. Rewriting our core infrastructure was fairly straightforward: as we have more engineers than we could possibly ever need or even know what to do with, we simply put a freeze on handling bug reports and shifted our effort to $ HYPED_TECHNOLOGY instead. We originally had some trouble with adapting to some of $ FLASHY_LANGUAGE’s quirks, and ran into a couple of bugs with $ HYPED_TECHNOLOGY, but overall their powerful new features let us remove some of the complexity that our previous solution had to handle.

There is absolutely no way Saagar Jha is poking at this or this.

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A First Look at `aspect-ratio`

Oh hey! A brand new property that affects how a box is sized! That’s a big deal. There are lots of ways already to make an aspect-ratio sized box (and I’d say this custom properties based solution is the best), but none of them are particularly intuitive and certainly not as straightforward as declaring a single property.

So, with the impending arrival of aspect-ratio (MDN, and not to be confused with the media query version), I thought I’d take a look at how it works and try to wrap my mind around it.

Shout out to Una where I first saw this. Boy howdy did it strike interest in folks:

Just dropping aspect-ratio on an element alone will calculate a height based on the auto width.

Without setting a width, an element will still have a natural auto width. So the height can be calculated from the aspect ratio and the rendered width.

.el {   aspect-ratio: 16 / 9; }

If the content breaks out of the aspect ratio, the element will still expand.

The aspect ratio becomes ignored in that situation, which is actually nice. Better to avoid potential data loss. If you prefer it doesn’t do this, you can always use the padding hack style.

If the element has either a height or width, the other is calculated from the aspect ratio.

So aspect-ratio is basically a way of seeing the other direction when you only have one (demo).

If the element has both a height and width, aspect-ratio is ignored.

The combination of an explicit height and width is “stronger” than the aspect ratio.

Factoring in min-* and max-*

There is always a little tension between width, min-width, and max-width (or the height versions). One of them always “wins.” It’s generally pretty intuitive.

If you set width: 100px; and min-width: 200px; then min-width will win. So, min-width is either ignored because you’re already over it, or wins. Same deal with max-width: if you set width: 100px; and max-width: 50px; then max-width will win. So, max-width is either ignored because you’re already under it, or wins.

It looks like that general intuitiveness carries on here: the min-* and max-* properties will either win or are irrelevant. And if they win, they break the aspect-ratio.

.el {   aspect-ratio: 1 / 4;   height: 500px;    /* Ignored, because width is calculated to be 125px */   /* min-width: 100px; */    /* Wins, making the aspect ratio 1 / 2 */   /* min-width: 250px; */ } 

With value functions

Aspect ratios are always most useful in fluid situations, or anytime you essentially don’t know one of the dimensions ahead of time. But even when you don’t know, you’re often putting constraints on things. Say 50% wide is cool, but you only want it to shrink as far as 200px. You might do width: max(50%, 200px);. Or constrain on both sides with clamp(200px, 50%, 400px);.

This seems to work inutitively:

.el {   aspect-ratio: 4 / 3;   width: clamp(200px, 50%, 400px); }

But say you run into that minimum 200px, and then apply a min-width of 300px? The min-width wins. It’s still intuitive, but it gets brain-bending because of how many properties, functions, and values can be involved.

Maybe it’s helpful to think of aspect-ratio as the weakest way to size an element?

It will never beat any other sizing information out, but it will always do its sizing if there is no other information available for that dimension.

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Core Web Vitals

Core Web Vitals is what Google is calling a a new collection of three web performance metrics:

  1. LCP: Largest Contentful Paint
  2. FID: First Input Delay
  3. CLS: Cumulative Layout Shift

These are all measurable. They aren’t in Lighthouse (e.g. the Audits tab in Chrome DevTools) just yet, but sounds like that’s coming up soon. For now, an open source library will get you the numbers. There is also a browser extension (that feels pretty alpha as you have to install it manually).

That’s all good to me. I like seeing web performance metrics evolve into more meaningful numbers. I’ve spent a lot of time in my days just doing stuff like reducing requests and shrinking assets, which is useful, but kind of a side attack to web performance. These metrics are what really matter because they are what users actually see and experience.

The bigger news came today though in that they are straight up telling us: Core Web Vitals matter for your SEO:

Today, we’re building on this work and providing an early look at an upcoming Search ranking change that incorporates these page experience metrics. We will introduce a new signal that combines Core Web Vitals with our existing signals for page experience to provide a holistic picture of the quality of a user’s experience on a web page.

Straight up, these numbers matter for SEO (or they will soon).

And they didn’t bury the other lede either:

As part of this update, we’ll also incorporate the page experience metrics into our ranking criteria for the Top Stories feature in Search on mobile, and remove the AMP requirement from Top Stories eligibility.

AMP won’t be required for SERP carousel thing, which was the #1 driver of AMP adoption. I can’t wait to see my first non-AMP page up there! I know some features will be unavailable, like the ability to swipe between stories (because that relies on things like the Google AMP cache), but whatever, bring it on. Let AMP just be a thing people use because they want to not because they have to.

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Background Patterns, Simplified by Conic Gradients

For those who have missed the big news, Firefox now supports conic gradients!

Starting with Firefox 75, released on the April 7, we can go to about:config, look for the layout.css.conic-gradient.enabled flag and set its value to true (it’s false by default and all it takes to switch is double-clicking it).

Screenshot. Shows the Firefox URL bar at `about:config`, a search for 'conic' giving the `layout.css.conic-gradient.enabled` flag as the sole result and its value set to `true`.
Enabling conic gradients in Firefox 75+

With that enabled, now we can test our CSS including conic gradients in Firefox as well.

While some of the demos in this article work just fine when using a polyfill, some use CSS variables inside the conic gradient and therefore require native support for this feature.

One thing I particularly like about conic gradients is just how much they can simplify background patterns. So let’s take a few linear-gradient() patterns from the gallery created by Lea Verou about a decade ago and see how we can now simplify them with conic-gradient!


Screenshot. Shows the original pyramid pattern with the code that was used to create it.
The pyramid pattern

The pattern above uses four linear gradients:

background:   linear-gradient(315deg, transparent 75%, #d45d55 0) -10px 0,   linear-gradient(45deg, transparent 75%, #d45d55 0) -10px 0,   linear-gradient(135deg, #a7332b 50%, transparent 0) 0 0,   linear-gradient(45deg, #6a201b 50%, #561a16 0) 0 0 #561a16; background-size: 20px 20px;

That’s quite a bit of CSS and perhaps even a bit intimidating. It’s not easy to just look at this and understand how it all adds up to give us the pyramid pattern. I certainly couldn’t do it. It took me a while to get it, even though gradients are one of the CSS features I’m most comfortable with. So don’t worry if you don’t understand how those gradients manage to create the pyramid pattern because, one, it is complicated and, two, you don’t even need to understand that!

Using conic-gradient(), we can now get the same result in a much simpler manner, with a single background layer instead of four!

What I like to do when coding repeating patterns is draw equidistant vertical and horizontal lines delimiting the rectangular boxes defined by the background-size. In this case, it’s pretty obvious we have square boxes and where their limits are, but it’s a really useful technique for more complex patterns.

Annotated screenshot. Shows the rectangles (squares in this case) defined by the `background-size`.
Highlighting the pattern’s cells

By default, conic gradients start from 12 o’clock and go clockwise. However, in our case, we want to offset the start of the gradient by 45° in the clockwise direction and afterwards make every one of the four shades occupy a quarter (25%) of the available space around the midpoint of our square box.

SVG illustration. Shows how we place a conic gradient into a single pattern cell by rotating the gradient start point 45° in the clockwise (positive) direction.
A pattern cell with a conic gradient’s hard stops at every 25% starting from 45° w.r.t. the vertical axis (live).

This means our pyramid pattern can be reduced to:

$ s: 20px; background:   conic-gradient(from 45deg,      #561a16 25%,      #6a201b 0% 50%,      #a7332b 0% 75%,      #d45d55 0%)      50%/ #{$ s $ s};

Not only does the code look simpler, but we’ve also gone from 260 bytes to 103 bytes, reducing the code needed to get this pattern by more than half.

We’re using the double position syntax as that’s also well supported these days.

We can see it in action in the Pen below:


Screenshot. Shows the original checkerboard pattern with the code that was used to create it.
The checkerboard pattern

This pattern above is created with two linear gradients:

background-color: #eee; background-image:   linear-gradient(45deg, black 25%, transparent 25%,      transparent 75%, black 75%, black),   linear-gradient(45deg, black 25%, transparent 25%,      transparent 75%, black 75%, black); background-size: 60px 60px; background-position: 0 0, 30px 30px;

Let’s see how we can simplify this CSS when replacing these linear gradients with a conic one!

Just like in the previous case, we draw vertical and horizontal lines in order to better see the rectangles defined by the background-size.

Annotated screenshot. Shows the rectangles (squares in this case) defined by the `background-size`.
Highlighting the pattern’s cells

Looking at the square highlighted in deeppink in the illustration above, we see that, in this case, our conic gradient starts from the default position at 12 o’clock. A quarter of it is black, the next quarter is dirty white and then we have repetition (the same black and then dirty white quarter slices once more).

SVG illustration. Shows how we place a conic gradient into a single pattern cell and then make it repeat after the 50% point.
A pattern cell with a conic gradient’s hard stops at every 25%, starting from the default at 12 o’clock and repeating after 50% (demo).

This repetition in the second half of the [0%, 100%] interval means we can use a repeating-conic-gradient(), which gives us the following code (bringing the compiled CSS from 263 bytes down to only 73 bytes – that’s reducing it by over 70%):

$ s: 60px; background:   repeating-conic-gradient(#000 0% 25%, #eee 0% 50%)      50%/ #{$ s $ s};

The Pen below shows it in action:

Diagonal checkerboard

Screenshot. Shows the original diagonal checkerboard pattern with the code that was used to create it.
The diagonal checkerboard pattern

Again, we have a pattern created with two linear gradients:

background-color: #eee; background-image:    linear-gradient(45deg, black 25%, transparent 25%,      transparent 75%, black 75%, black),   linear-gradient(-45deg, black 25%, transparent 25%,      transparent 75%, black 75%, black); background-size: 60px 60px;

We draw horizontal and vertical lines to split this pattern into identical rectangles:

Annotated screenshot. Shows the rectangles (squares in this case) defined by the `background-size`.
Highlighting the pattern’s cells

What we now have is pretty much the same checkerbox pattern as before, with the sole difference that we don’t start from the default position at 12 o’clock, but from 45° in the clockwise direction.

If you’re having trouble visualising how simply changing the start angle can make us go from the previous pattern to this one, you can play with it in the interactive demo below:

Note that this demo does not work in browsers that have no native support for conic gradients.

This means our code looks as follows:

$ s: 60px; background:   repeating-conic-gradient(from 45deg,      #000 0% 25%, #eee 0% 50%)    50%/ #{$ s $ s};

We can see it in action below:

Again, not only is the code simpler to understand, but we’ve also gone from 229 bytes to only 83 bytes in the compiled CSS, reducing it by almost two-thirds!


Screenshot. Shows the original Half-Rombes pattern with the code that was used to create it.
The half-rombes pattern

This pattern was created with four linear gradients:

background: #36c; background:   linear-gradient(115deg, transparent 75%, rgba(255,255,255,.8) 75%) 0 0,   linear-gradient(245deg, transparent 75%, rgba(255,255,255,.8) 75%) 0 0,   linear-gradient(115deg, transparent 75%, rgba(255,255,255,.8) 75%) 7px -15px,   linear-gradient(245deg, transparent 75%, rgba(255,255,255,.8) 75%) 7px -15px,   #36c; background-size: 15px 30px;

Just like in the previous cases, we draw equidistant vertical and horizontal lines in order to better see the repeating unit:

Annotated screenshot. Shows the rectangles (squares in this case) defined by the `background-size`.
Highlighting the pattern’s cells.

What we have here is a pattern that’s made up of congruent isosceles triangles (the angled edges are equal and the dark blue triangles are a reflection of the light blue ones) formed by the intersection of equidistant parallel lines that are either horizontal, angled clockwise, or the other way. Each of these three types of parallel lines is highlighted in the illustration below:

Illustration. Shows the equidistant parallel lines which create the pattern of isosceles triangles.
Parallel guides

Every pattern cell contains a full triangle and two adjacent triangle halves in the upper part, then a reflection of this upper part in the lower part. This means we can identify a bunch of congruent right triangles that will help us get the angles we need for our conic-gradient():

SVG illustration. Shows how we place a conic gradient into a single pattern cell by rotating the gradient start point by an angle β in the clockwise (positive) direction such that the 0% line goes through the top right corner and then all the other hard stops are either horizontal or going through the cell corners.
A pattern cell with a conic gradient’s hard stops such that they’re either horizontal or go through the cell corners, all starting from β w.r.t. the vertical axis (demo)

This illustration shows us that the gradient starts from an angle, β, away from the default conic gradient start point at 12 o’clock. The first conic slice (the top right half triangle) goes up to α, the second one (the bottom right dark triangle) up to 2·α, and the third one (the bottom light triangle) goes halfway around the circle from the start (that’s 180°, or 50%). The fourth one (the bottom left dark triangle) goes to 180° + α and the fifth one (the top left light triangle) goes to 180° + 2·α, while the sixth one covers the rest.

SVG illustration. Highlights the right triangle from where we can get α knowing the catheti and shows how we can then compute β.
Getting α and β (demo)

From the highlighted right triangle we get that:

tan(α) = (.5·h)/(.5·w) = h/w

Knowing the width (w) and height (h) of a pattern cell, we can get the angles α and β:

α = atan(h/w) β = 90° - α

It results in the pattern that’s generated by the following code:

$ w: 15px; $ h: 30px; $ a: atan($ h/$ w)*180deg/pi(); $ b: 90deg - $ a; $ c0: #36c; $ c1: #d6e0f5;  html {   background:      conic-gradient(from $ b,        $ c1 0% $ a,        $ c0 0% 2*$ a,        $ c1 0% 50%,        $ c0 0% 180deg + $ a,        $ c1 0% 180deg + 2*$ a,        $ c0 0%)      0 0/ #{$ w $ h}; }

This means going from 343 bytes to only 157 bytes in the compiled CSS. The result can be seen below:

You can tweak the pattern width ($ w) and height ($ h) in the Sass code in order to see how the pattern gets squished and stretched for different aspect ratios.

In the particular case where the angle between 2*$ a and 50% (or 180deg) is also $ a, it results that $ a is 60deg, our isosceles triangles are equilateral, and our gradient can be reduced to a repeating one (and under 100 bytes in the compiled CSS):

$ a: 60deg; $ b: 90deg - $ a; $ w: 15px; $ h: $ w*tan($ a); $ c0: #36c; $ c1: #d6e0f5;  html {   background:      repeating-conic-gradient(from $ b,        $ c1 0% $ a, $ c0 0% 2*$ a)      0 0/ #{$ w $ h} }

The live result can be seen below:

Bonus: Intersecting line backgrounds!

Screenshot. Shows the original intersecting lines pattern with the code that was used to create it.
Intersecting line background examples

While these are not repeating patterns, they’re examples of a situation where a single conic gradient achieves an effect that would have previously needed a bunch of linear ones.

What we have here is a conic-gradient() created starting from two straight lines intersecting within the rectangular box where we set the background.

SVG illustration. Shows a rectangular box and two random lines intersecting inside it. This intersection point (x,y) is the point the conic gradient goes around, while the gradient's start is from the angle β formed by the line segment closest to the top right corner with the vertical. The hard stops are at α, the angle between the start segment and the next one in clockwise order, at 50% and at 180° + α.
Bonus pattern structure (ldemo)

The gradient goes around the point of coordinates, x,y, where the two straight lines intersect. It starts from an angle, β, which is the angle of the line segment that’s closest to the top-right corner, then has hard stops at α, 50% (or 180°) and 180° + α.

If we want to have multiple elements with similar such patterns created with the help of different intersecting lines and different palettes, we have the perfect use case for CSS variables:

.panel {   background:      conic-gradient(from var(--b) at var(--xy),        var(--c0) var(--a), var(--c1) 0% 50%,        var(--c2) 0% calc(180deg + var(--a)), var(--c3) 0%); }

All we have to do is set the position (--xy), the start angle (--b), the first angle (--a) and the palette (--c0 through --c3).

.panel {   /* same as before */      &:nth-child(1) {     --xy: 80% 65%;      --b: 31deg;     --a: 121deg;      --c0: #be5128;     --c1: #ce9248;     --c2: #e4c060;     --c3: #db9c4e   }      /* similarly for the other panels */ }

Instead of hardcoding, we could also generate these values randomly or extract them from a data object with the help of a CSS or HTML preprocessor. In this second case, we’d set these custom properties inline, which is precisely what I did in the Pen below:

Since we’re using custom properties inside the conic gradients, this demo does not work in browsers that don’t support them natively.

Well, that’s it! I hope you’ve enjoyed this article and that it gives you some ideas about how conic gradients can make your life easier.

The post Background Patterns, Simplified by Conic Gradients appeared first on CSS-Tricks.


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PureCSS Gaze

Diana Smith with another mind-bending all HTML & CSS painting.

I love that these occupy a special place on the “Should I draw this in CSS?” curve. Things like simple shapes are definitely on the “yes” side of the curve. Then there’s a large valley where things get a little too impractical to draw that way, and using some other image format (e.g. SVG) makes way more sense.

Diana’s work pulls the curve back up to the “yes” side. Not only because it’s proof that CSS can be an amazing expressionistic art tool, but also from a performance standpoint — it’s only 2 KB of HTML and 10 KB of CSS.

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