Tags: methodology



Programming CSS

There’s a worrying tendency for “real” programmers look down their noses at CSS. It’s just a declarative language, they point out, not a fully-featured programming language. Heck, it isn’t even a scripting language.

That may be true, but that doesn’t mean that CSS isn’t powerful. It’s just powerful in different ways to traditional languages.

Take CSS selectors, for example. At the most basic level, they work like conditional statments. Here’s a standard if statement:

if (condition) {
// code here

The condition needs to evaluate to true in order for the code in the curly braces to be executed. Sound familiar?

condition {
// styles here

That’s a very simple mapping, but what if the conditional statement is more complicated?

if (condition1 && condition2) {
// code here

Well, that’s what the decendant selector does:

condition1 condition2 {
// styles here

In fact, we can get even more specific than that by using the child combinator, the sibling combinator, and the adjacent sibling combinator:

  • condition1 > condition2
  • condition1 ~ condition2
  • condition2 + condition2

AND is just one part of Boolean logic. There’s also OR:

if (condition1 || condition2) {
// code here

In CSS, we use commas:

condition1, condition2 {
// styles here

We’ve even got the :not() pseudo-class to complete the set of Boolean possibilities. Once you add quantity queries into the mix, made possible by :nth-child and its ilk, CSS starts to look Turing complete. I’ve seen people build state machines using the adjacent sibling combinator and the :checked pseudo-class.

Anyway, my point here is that CSS selectors are really powerful. And yet, quite often we deliberately choose not to use that power. The entire raison d’être for OOCSS, BEM, and Smacss is to deliberately limit the power of selectors, restricting them to class selectors only.

On the face of it, this might seem like an odd choice. After all, we wouldn’t deliberately limit ourselves to a subset of a programming language, would we?

We would and we do. That’s what templating languages are for. Whether it’s PHP’s Smarty or Twig, or JavaScript’s Mustache, Nunjucks, or Handlebars, they all work by providing a deliberately small subset of features. Some pride themselves on being logic-less. If you find yourself trying to do something that the templating language doesn’t provide, that’s a good sign that you shouldn’t be trying to do it in the template at all; it should be in the controller.

So templating languages exist to enforce simplicity and ensure that the complexity happens somewhere else. It’s a similar story with BEM et al. If you find you can’t select something in the CSS, that’s a sign that you probably need to add another class name to the HTML. The complexity is confined to the markup in order to keep the CSS more straightforward, modular, and maintainable.

But let’s not forget that that’s a choice. It’s not that CSS in inherently incapable of executing complex conditions. Quite the opposite. It’s precisely because CSS selectors (and the cascade) are so powerful that we choose to put guard rails in place.

Problem space

Adam Wathan wrote an article recently called CSS Utility Classes and “Separation of Concerns”. In it, he documents his journey through different ways of thinking about CSS. A lot of it is really familiar.

Phase 1: “Semantic” CSS

Ah, yes! If you’ve been in the game for a while then this will be familiar to you. The days when we used to strive to keep our class names to a minimum and use names that described the content. But, as Adam points out:

My markup wasn’t concerned with styling decisions, but my CSS was very concerned with my markup structure.

Phase 2: Decoupling styles from structure

This is the work pioneered by Nicole with OOCSS, and followed later by methodologies like BEM and SMACSS.

This felt like a huge improvement to me. My markup was still “semantic” and didn’t contain any styling decisions, and now my CSS felt decoupled from my markup structure, with the added bonus of avoiding unnecessary selector specificity.


But then Adam talks about the issues when you have two visually similar components that are semantically very different. He shows a few possible solutions and asks this excellent question:

For the project you’re working on, what would be more valuable: restyleable HTML, or reusable CSS?

For many projects reusable CSS is the goal. But not all projects. On the Code For America project, the HTML needed to be as clean as possible, even if that meant more brittle CSS.

Phase 3: Content-agnostic CSS components

Naming things is hard:

The more a component does, or the more specific a component is, the harder it is to reuse.

Adam offers some good advice on naming things for maximum reusability. It’s all good stuff, and this would be the point at which I would stop. At this point there’s a nice balance between reusability, readability, and semantic meaning.

But Adam goes further…

Phase 4: Content-agnostic components + utility classes

Okay. The occasional utility class (for alignment and clearing) can be very handy. This is definitely the point to stop though, right?

Phase 5: Utility-first CSS

Oh God, no!

Once this clicked for me, it wasn’t long before I had built out a whole suite of utility classes for common visual tweaks I needed, things like:

  • Text sizes, colors, and weights
  • Border colors, widths, and positions
  • Background colors
  • Flexbox utilities
  • Padding and margin helpers

If one drink feels good, then ten drinks must be better, right?

At this point there is no benefit to even having an external stylesheet. You may as well use inline styles. Ah, but Adam has anticipated this and counters with this difference between inline styles and having utility classes for everything:

You can’t just pick any value want; you have to choose from a curated list.

Right. But that isn’t a technical solution, it’s a cultural one. You could just as easily have a curated list of allowed inline style properties and values. If you are in an environment where people won’t simply create a new utility class every time they want to style something, then you are also in an environment where people won’t create new inline style combinations every time they want to style something.

I think Adam has hit on something important here, but it’s not about utility classes. His suggestion of “utility-first CSS” will only work if the vocabulary is strictly adhered to. For that to work, everyone touching the code needs to understand the system and respect the boundaries of it. That understanding and respect is far, far more important than any particular way of structuring HTML and CSS. No technical solution can replace that sort of agreement …not even slapping !important on every declaration to make them immutable.

I very much appreciate the efforts that people have put into coming up with great naming systems and methodologies, even the ones I don’t necessarily agree with. They’re all aiming to make that overlap of HTML and CSS less painful. But the really hard problem is where people overlap.