Photo by Nikita Kachanovsky on Unsplash

I was excited about Scoped CSS when frameworks like React and Vue introduced them a few years back.

As I began trying Scoped CSS out for myself, I was disappointed and felt it didn’t live up to its hype.

But after more tries, I’m happy to announce that Scoped CSS is indeed useful. You only have to realize its limitations and what to do when you face them.

I’m Not Talking About the Native CSS :scope

Before you continue further, I want to make sure we’re talking about the same thing.

In this article, I’m talking about Scoped CSS, which can be found in major frameworks like React, Vue, Svelte, and Astro.

I’m not talking about the native CSS :scope. You can find out more about that here.

The Premise of Scoped CSS

Scoped CSS was one of the biggest features that frameworks provided us with. It promises to restrict the scope of your CSS so your CSS would not leak into other components.

The limitations of Scoped CSS are as follows:

  1. You cannot style children components
  2. You cannot style slot content

Now, let’s see what I mean by these limitations.

You Cannot Style Children Components

From my experience, Scoped CSS in all frameworks behaves in the same manner. So, I’m going to use Svelte here to illustrate my point.

Let’s say I imported a SVG component, and I’d like to style the SVG from a Menu component. Here’s what that code looks like:

<script>
  import SVG from './SVG.svelte'
</script>

<div class="Menu">
  <SVG />
  <span>Menu</span>
</div>

The SVG component contains the SVG and nothing more.

<!-- SVG component -->
<svg>...</svg>

If I try to style the SVG from the Menu component, the styles will not be applied.

<!-- Menu component -->
<style>
  .Menu svg path {
    stroke: red;
  }
</style>
SVG is still colored black

And I’m forced to use the global or the global selector to style this SVG.

<!-- Global attribute -->
<style global>
  .Menu svg path {
    fill: red;
  }
</style>

<!-- Global selector -->
<style>
  :global(.Menu svg path) {
    fill: red;
  }
</style>
SVG is still colored red

The Global Attribute

The global attribute negates scoped CSS and allows the entire style block to act like Normal CSS.

<style global>
  .Menu svg path {
    fill: red;
  }
</style>

Using the global attribute isn’t a great practice because you might as well write Normal CSS instead.

By the way, if you use Astro, the global attribute is a directive and not an attribute.

<style is:global>
  …
</style>

The Global Selector

The :global() selector allows you to expose the values wrapped inside it to the global scope.

<style>
  :global(.Menu svg path) {
    fill: red;
  }
</style>

If you want to keep .Menu in the local scope, you can use :global only on the rest of the selectors.

<style>
  .Menu :global(svg path) {
    fill: red;
  }
</style>

This is nice.

But there’s a huge problem.

The global selector cannot be used in the middle of the selector chain. So this doesn’t work.

<style>
  /* These don’t work */
  .Menu :global(svg) path { … }
</style>

Because the global selector cannot be used in the middle of the selector chain, nesting doesn’t work as well.

<style lang="“scss”">
  /* This doesn’t work */
  .Menu :global(svg) {
    path { … }
  }
</style>

This gives Scoped CSS a big minus point in my world.

You Cannot Style Slot Content

Scoped CSS is also limited when you have to style slot content.

For this, let’s say we have an <Article> component, and we are going to pass the contents through a <slot>.

<article class="Article">
  <slot />
</article>

We’ll use <Article> like the following:

<script>
  import Article from './Article.svelte'
</script>

<article>
  <h2>This is a header</h2>
  <p>This is a paragraph</p>
</article>

If you try to style the slot content from Article with Scoped CSS, you’ll realize it doesn’t work.

<article class="Article">
  <slot />
</article>

<style>
  h2 {
    color: blue;
  }
  p {
    color: red;
  }
</style>
h2 and p are still black

You need to use the global attribute or the global selector instead.

Styling Slot Content

You can use global selectors or the global attribute to style slot content.

In this case, let’s go with global selectors.

Here’s how I would style the slot content:

<article class="Article">
  <slot />
</article>

<style lang="scss">
  article {
    :global(h2) {
      color: blue;
    }
    :global(p) {
      color: red;
    }
  }
</style>
h2 and p are now coloured

When you use global selectors to style slot content, pay attention to these points:

One: global must be written for every selector you wish to target. If you have to use a large number of global selectors, it may be worthwhile to write normal CSS instead:

Two: :global should come AFTER a selector (article in this case). If :global doesn’t come after a selector, you’ll be writing CSS into the global scope, which is probably not what you want.

If you did what I just mentioned, your selectors should look somewhat like this:

How a scoped selector looks in the devtools

Wrapping Up

Scoped CSS is a great future.

Scoped CSS can be frustrating to use when you don’t know what its limitations are.

Once you know the limitations, you can use Scoped CSS to its fullest potential.

Further Reading

By the way, this article was originally written on my blog.

Feel free to visit that if you want to have these articles delivered to your email when they’re released! 🙂.

Limitations of Scoped CSS was originally published in Better Programming on Medium, where people are continuing the conversation by highlighting and responding to this story.

Previous Post
Next Post