critical VS styled-system

If the link element is placed inside of the shadow DOM, then it's not render blocking and you will experience a flash of unstyled content. That's what the lit docs are referring to.

If you place the link element inside the head of your document, then it is render blocking, which means the browser has to make two round trips to the server if the CSS file isn't in the cache before it render (one to download the HTML file, and then another after it discovers your link element, and has to download the corresponding CSS file).

> The best from both worlds is to embed a lightweight basic CSS stylesheet inline and the rest in cache-able external CSS files.

This is the absolute optimal way of doing it. You would have to analyze your styles to see which styles are applied to elements above the fold, then extract them and put them in an inline style tag. The rest of the styles would have to be downloaded via a link tag, but you'd have to place the link tag at the very end of the HTML body tag to prevent the browser from blocking as soon as it encounters the link element or alternatively use JavaScript to add the link element after the page has been rendered. There are tools to automate this for static sites [1], but doing this for dynamically generated HTML is kind of a pain, and I've found that browsers parse CSS so quickly that the overhead of just inlining it all is very low in many cases.

[1] https://github.com/addyosmani/critical

CLS is a pain in the arse. Extract your critical CSS and inline it https://github.com/addyosmani/critical although doing critical CSS badly makes things worse.

There is a tool that allows generating critical CSS and determining which CSS is critical and which is not. It helps to separate it into files, and there is also an npm package for that.

I am a fan of CSSWizardry and yet I find this post misleading. The examples shown are ways NOT to do frontend performance engineering.

The current best performant way to load JS is asynchronously as documented at https://web.dev/efficiently-load-third-party-javascript/.

And the best way to load CSS is with Critical Path CSS + Async CSS as documented at https://web.dev/defer-non-critical-css/.

The easiest way to generate Critical CSS is https://github.com/addyosmani/critical where you may suggest multiple resolutions.

I have found https://github.com/addyosmani/critical-path-css-tools to be a great resource to master critical path CSS which improves page render speeds. It helps build fast rendering sites, sometimes even sub-second renders given you have a low latency backend.

CSSOM tree has to be built before start rendering the page. To build it, the browser has to parse the CSS first. I said parse and not load because your CSS can be inlined (in a tag).

CSS is render-blocking, which means you can't start rendering the page until it's parsed. But it's not parser-blocking, which means the browser can continue parsing the HTML while the CSS is being downloaded (if it was linked externally).

The main takeaway here is that the larger your CSS file is the longer it will take to start rendering the page because it's a render-blocking resource.

Loading JavaScript

JavaScript is a parser-blocking resource. This means once the browser finds any JavaScript code, it will stop parsing immediately to download and execute the JavaScript. After the JavaScript is executed, the parser can continue parsing the document.

So JavaScript can delay rendering because the browser can't complete building the DOM until it has parsed the HTML.

JavaScript has to wait for CSSOM

To make things even worse, your JavaScript code can't start executing if there's CSS being downloaded. In other words, if you have Optimizing your page load time

Now we get to the fun part; making our pages load faster.

Getting into the details of each technique is beyond the scope of this article, but I will give you a quick overview of each one. After that, it should be easier to learn more about each one on your own.

Only load the used/critical CSS

Most of the time we load CSS that we don't need in the current page. So, we can split the CSS file into smaller ones and use each one based on what the current page needs.

A common case we can apply this to is loading some third party CSS code only in the pages that need them. For example, only use the code syntax highlighter CSS library on the pages that display code.

There's also a well-known technique called critical CSS. It's used to load only the CSS code that you see above the fold (the visible part of the browser on the initial load), and then lazy-load the rest asynchronously. And you can make this even better by inlining the critical CSS and lazy-load the rest externally.

Loading JavaScript asynchronously

Two popular attributes to achieve this: defer and async. Using either will not cause the browser to wait until they are downloaded to continue parsing.

The main difference between them is the time and order of execution.

Defer scripts start executing after the whole DOM is constructed but before DOMContentLoaded event is fired. This also means you should see the page rendered before executing the script.

Defer scripts execute in the order they were defined. So if script1 is above script2, script1 will always start executing before script2 even if script2 is loaded before.

Async scripts will start execute as soon as they are fetched. Async scripts don't wait for the DOM to be constructed, which means they can block the parser if an async script is fetched before the DOM is built.

Async scripts execute in the order they were fetched. The one that loads first executes first.

The rule of thumb is to use defer scripts when they depend on the content (DOM) of the page, and use async scripts for things that don't need the DOM such as analytics, etc.

Minify and compress resources

There are many build tools that help you minify your CSS and JavaScript. Minification is the process of removing any unnecessary characters for execution like spaces, comments, etc.

Compressing your resources is done by the server. gzip and brotli and the most popular compression types nowadays.

Minifying and compressing your resources will make them much smaller, which will improve your loading time.

Preloading important resources

The browser fetches the resources as it finds them while parsing the HTML. Sometimes it would be useful if we request these resource as soon as possible even before the parser finds them.

An example would be having two synchronous external JavaScript files below each other. If we don't use preload, then we have to wait for the first script to load and execute before loading the second one. But with preload we can tell the browser to fetch that second script even while it's parsing the HTML.

Preloading is also used for fetching other resources like CSS, images, fonts, etc.

Preloading can be done with . Example:

 rel="preload" href="style.css" as="style">
 rel="preload" href="main.js" as="script">

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Reduce your server response time

No matter how many optimization you do to your client code, it will not make your page load faster if your server takes a long time to send the requested HTML code.

Usually this is the least we can control especially if we don't maintain the backend code. But if we do, we can do things like optimizing the database queries (how fast we pull data from our database), using caching, compressing and minifying responses, upgrading the server hardware, etc.

Now you can learn more

In this article we barely scratched the surface of loading performance optimizations. But it should be easier now to dive deeper into each one as you should have a full understanding of how the browser loads pages.

An important part we didn't touch in this article is the tools we can use to measure the performance of the page and the impact of the optimizations we do. Google Chrome provides us with two good tools for this: the performance tab in the devtools and Lighthouse. So I encourage you to check them on your own.

A while ago I'd noticed that the version (or configuration) of the Critical packaged used by my Netlify build plugin was missing that fallback, so I manually added it to my Eleventy template, no big deal.

Defer or async css/js files — Don’t make leads wait for unnecessary files to download before showing something. In the case of CSS, there are a few tools for in-lining only what’s above-the-fold into your html.

Consider automating the process of extracting and inlining "Above the Fold" CSS using the Critical tool.

Critical CSS build by Addy Osmani is a useful library that extracts and inlines critical-path CSS in HTML pages.

KumaUI : Another relatively new contender, Kuma uses zero runtime CSS-in-JS to create headless UI components which allows a lot of flexibility. It was heavily inspired by other zero runtime CSS-in-JS solutions such as PandaCSS, Vanilla Extract, and Linaria, as well as by Styled System, ChakraUI, and Native Base. ### Vue

Then we started using Chakra, which has style props based on Styled System. I'm quite happy with them after about a year.

Your repo still links to styled-system.com, are you planning on hosting your own docs?

But yeah, Tailwind fanboys do hate it, because Chakra needs some initial time to research and understand how it works under the hood. And then it gets super easy and intuitive to use. It's an implementation of a general concept abstraction called styled-system, I advise anyone to start their learning about Chakra from there: https://styled-system.com/

Note how each class in the atomic version maps to just a single CSS property and value. In fact, if I hadn’t included the second block, I bet you’d have had no problem determining each class’ effect from the markup alone! This is a hallmark of atomic CSS — the effect of a class is typically self evident from its name alone, whereas the specifics of a class name like media are more ambiguous.

For anyone familiar with atomic CSS today, the example above will likely appear unremarkable. The transition towards this approach was anything but, however — and on some corners of the web today, debate still rages about whether atomic CSS has been the best or worst thing to happen to styling on the web since CSS.

There was, however, clearly an appetite for this approach amongst a non-trivial swath of web developers: the year 2014 saw the release of both Adam Morse’s Tachyons and Brent Jackson’s Basscss, the first two frameworks to go all-in on atomic CSS. These frameworks were instrumental in writing the blueprints for the atomic CSS methodology and turning the status quo on its head — and indeed, the shift was so monumental that, within a number of years, ‘utility-first’ CSS frameworks started becoming multimillion dollar businesses.

The atomization of CSS had officially begun.

Atomic CSS: successes and perceived failures

In order to understand the success of atomic CSS (even if that success remains a point of debate in some circles), we should first examine its principles, and the goals those principles seek to achieve. Many of these principles are derived from functional programming, hence the alternative name ‘functional CSS’. Additional inspiration came from the Unix philosophy.

The most fundamental principles of atomic CSS are:

Classes should have a single purpose.

Classes should do one thing, and they should do it well. This makes each class more reusable. A class that applies a margin, and only a margin, is more reusable than a class that applies and margin and a text colour.

A class’ effect should be self evident.

There should be no mystery about the effect of using a class — clarity should always trump cleverness. The effect of a class named flex which sets the display property to flex is self evident. The effect of a class named media which may set any number of property values is ambiguous.

Classes should be composable.

Complex styles should be achieved by composing multiple single purpose classes together, rather than by writing new, complex, and less reusable classes.

Classes should be immutable and free of side effects.

For example, the underline class should only ever apply an underline style. It should never not apply the underline, or apply another style, or change any other property of any other element. Under no circumstances should it change the effect of another class.

It’s important to note that these principles were not devised for their own sake — each plays an important role in authoring performant, maintainable, robust styles:

• Single purpose classes are more reusable and composable than multipurpose classes. Thus, single purpose classes provide greater flexibility as well as reduced CSS file sizes, both at the outset of new projects and throughout their lifecycle (as fewer styles need to be added to deliver iterations and additions to UI).

• Classes with singular, self evident effects reduce cognitive overhead for developers; the resultant styling systems are thus easier to learn, and this in turn helps frontend teams scale their efforts across people and time.

• Classes which are immutable and free of side effects result in fewer bugs — and where bugs occur, easier debugging and resolution follows.

In these ways and in others, I have always felt that the nature of atomic CSS flows very much with the grain of CSS itself. Remember that CSS was designed to be independent of markup, and atomic CSS is by design untethered to any particular markup structure or content based semantics. Atomic CSS also honors CSS’ specificity algorithm rather than attempting to game it — it does not concern itself with optimized selector ranking or scope, since every class is of single purpose and equal specificity. This also means CSS’ inheritance model becomes an advantage as it was originally intended: compositions can be built up with inheritance in mind, over several layers of markup.

There are, however, many common objections raised against the atomic CSS methodology. In general, these tend to be:

’It’s not semantic.’

We’ve touched on this already, but it’s worth repeating: semantics, accessibility, and clarity do matter, but with all due respect to Zeldman, there is nothing inherently unsemantic, inaccessible, or unclear about ‘visual class names’, nor is there a reason for CSS to map to the same semantics as HTML.

‘This is inline styles all over again.’

Nope. Inline styles are defined in HTML; atomic classes are defined in a style sheet. Inline styles do not permit media queries, pseudo elements, or pseudo classes; atomic classes do. Inline styles have a specificity ranking of 1-0-0-0, which can only be outranked by !important; atomic classes have a specificity of 0-0-1-0, the same as any single class. An inline style’s source of truth is its own singular invocation on a given element; an atomic class’ source of truth is a style sheet. There is a lexical resemblance between class='red' and style='color: red'; this is where the similarities end.

‘Putting so many classes on my elements looks ugly/is hard to read.’

Admittedly, doesn’t read like poetry (and yes, that snippet is taken from this very page as of this writing). However, something that is a delight is being able to rapidly iterate on this composition — from the logical origin of that composition (the markup), whether in the browser or my editor — to explore different combinatorial spaces within the bounds of a design system. Iterating in this fashion simply cannot be matched when using other methodologies.

‘This is so not DRY.’

It’s true, atomic CSS can lead to repeating declarations of various styling rules — but I vastly prefer repeating declarations to repeating definitions (which, in my experience, are much harder to maintain). Also, remember that every time you repeat a class name, that’s one more addition you didn’t have to make to your style sheet! Ultimately, this is a matter of choosing what kind of repetition you want, not one of avoiding repetition altogether.

‘Atomic CSS is at odds with modern component modeling.’

‘Thinking in React’ is one of those articles that changed the way I thought about web development when it was published, and there’s no denying that building frontends on the web has become a component centric process. However, it’s important to differentiate the process of thinking in components and the process of styling components. A conceptual abstraction does not require an equivalent material abstraction, and the fact of a component’s existence does not necessitate a dedicated CSS class.

‘This still doesn’t solve the problem of global scope or one off styles.’

It doesn’t, and in fact atomic CSS is not designed for this. For scoped or one off styles, a different approach is absolutely required.

Atomic CSS can provide a fantastic foundation that covers the vast majority of styling needs for a given website and its constituent components, and it can deliver those styles in a fraction of the file size and complexity of other methodologies. To be clear, these claims are not theoretical: this has been my experience both as a contributor and leader of frontend teams over the past 8 years, and the same has been true for many others both within and outside of my professional circle. But as we’ve noted, atomic CSS doesn’t cover every use case: scoped and one off styles are not part of its wheelhouse. So what’s to be done when a need for these sorts of styles emerges?

Going bespoke

Photo by Chris Ralston on Unsplash

Where one off styles are needed, or where we want to ensure certain styles are scoped to a given component, additional measures beyond an atomic CSS methodology will be required. There are several techniques that can be used to address these concerns, with a few notable examples having become more popular in recent years:

CSS in JS

The obvious contender in this list. I used CSS in JS for many years myself, and have to say the developer ergonomics are pretty impressive, as is the ability to leverage both repeatable and bespoke, scoped styles (especially when using libraries like Styled System or Theme UI). Unfortunately, great developer ergonomics and scoping are not enough. CSS in JS can add significant weight to client side bundles, along with increased setup complexity (especially when server side rendering is involved). Some solutions can also lock you in to certain frontend frameworks, limiting the portability of your styles. There are some solutions emerging to address these concerns (e.g. Vanilla Extract), but at the end of the day, I admit I’m growing tired of learning abstractions of CSS — there are so many more valuable things I could be doing with my time. This isn’t necessarily a popular opinion, but I think CSS is actually pretty amazing on its own, and the closer to the metal I can stay, the happier I am.

CSS Modules

The name may suggest that CSS Modules are part of the CSS spec, but this is not the case. CSS Modules allow authors to extract styles from a vanilla .css file and into a JavaScript file containing markup; at build time, these extracted styles are then regenerated as locally scoped styles wherever they are used. This seems to offer some of the benefits of CSS in JS, but without the ergonomics of colocating styles, content, and behavior within a given component.

Shadow DOM

Shadow DOM is a web standards specification which is designed to provide encapsulation of content, styles, and behavior — but it has a number of hard to swallow caveats. For one, Shadow DOM roots need to be initialized in JavaScript (though Declarative Shadow DOM should address this in the future.) Further, styling encapsulation doesn’t work quite like you think it does, and this can cause some headaches. I believe the Shadow DOM holds promise, but for many use cases, it can end up being more trouble than it’s worth.

Fortunately, a compelling solution for dealing with scoped and one off styles exists in the form of HTML custom elements, which are part of the web components spec along with Shadow DOM and HTML templates. I may be biased, but I think the best way to work with custom elements right now is with Enhance (though to be fair, I got a sneak peak at Enhance before joining Begin in 2022, and was just as enthusiastic at that time).

Using Enhance to author custom elements in the form of Single File Components (SFCs) has a number of huge benefits:

1. Custom elements are expanded on the server, providing great performance and an excellent baseline for progressive enhancement on the client.

2. Locally scoped, one off styles can be authored simply by including a </code> block in your SFC. When your component is expanded on the server, these style blocks will be hoisted into the document head, with all of that style block’s selectors scoped to your custom element. This allows for one off styles to be encapsulated and scoped to the component they’re authored in, without needing to touch the Shadow DOM. Scoped styles written within an SFC are also a great place to leverage strategies like <a href="https://css-tricks.com/are-we-in-a-new-era-of-web-design-what-do-we-call-it/">intrinsic design</a>, which can happily coexist alongside a global, atomic class system.</p></li> <li><p>If you don’t need to write client side behavior, <strong>you never have to interface with JavaScript classes or the <a href="https://developer.mozilla.org/en-US/docs/Web/API/CustomElementRegistry">Custom Elements Registry</a></strong>. This is particularly handy for engineers (or designers) who might excel at HTML and CSS but lack experience in JavaScript. Although SFCs are authored as JavaScript functions, the bulk of the authored code is written in HTML and CSS, as seen below:<br> </p></li> </ol> <div class="highlight js-code-highlight"> <pre class="highlight javascript"><code><span class="c1">// my-button.mjs</span> <span class="k">export</span> <span class="k">default</span> <span class="kd">function</span> <span class="nx">MyButton</span><span class="p">({</span> <span class="nx">html</span> <span class="p">})</span> <span class="p">{</span> <span class="k">return</span> <span class="nx">html</span><span class="s2">` <style> /* One off styles applied only to button elements rendered by MyButton. */ /* Any button outside this component will not be affected. */ button { appearance: none; box-shadow: 0 2px 4px rgba(0,0,0,0.1); } ` } // index.html <my-button>Click Me!</my-button>

I find css-as-props is better than a huge string of classes, as it much more readable and statically analyzable. I wonder if anyone is working on a successor to styled-system (though it works fine).

[1] https://styled-system.com/

My goal was to try a few new libraries and get experience under my belt (cause isn’t that what dev blogs are for?). I’d swap out Gatsby for **Astro,** and Styled Components + Styled System for **Vanilla Extract**. I was interested in trying Astro as it just hit 1.0, and I’ve been experimenting for a while with Vanilla Extract as a way to write Typescript powered styles and export to CSS.

I'm a huge fain of Tailwind but if you're using react you can also consider styled-system:

https://styled-system.com

It seems to have a lot of the benefits of Tailwind but better integration with Typescript.

Our app is a little odd. It's a very specialized version of something like Wix or Squarespace for use in a particular niche. The majority of our front end code is our own component library, really, and we use styled-components along with what will soon be a custom fork of this now sadly abandoned project: https://styled-system.com/. Styled system is great for us because it allows our users to do extensive, responsive theming in ways we define and keep from being ugly when touched by non-coders on a component by component basis.

Restyle is my personal favorite. It’s strongly inspired by the amazing, albeit a bit outdated, styled-system for web, but is fully type-safe and has amazing customization options.