The future direction of CSS

When will plain CSS be good enough to replace Sass, Less, Stylus, and rest?

One of the toughest facts that web developers have to face is that most people still use old, low-performance browsers when browsing websites. Browsers are adding new features all the time, but you usually can't take advantage of them unless you're willing to lose a lot of users who haven't updated their browsers.

This problem does not exist when you use Electron to develop applications. Because the code of the Electron application you wrote runs on a separate Chromium browser. Chromium is the core engine of Google Chrome and is powered by Google. At the same time, it is also open source, which means that a large number of developers in the community are optimizing it every day.

CSS custom properties

Last week, Electron released a new version that supports CSS custom properties. If you've used preprocessing languages ​​like Sass and Less, you're probably already familiar with variables, which allow you to define reusable values ​​for things like color schemes or layouts. Variables keep your stylesheet DRY (Don't Repeat Yourself) and improve maintainability.

Since CSS custom properties are just regular CSS properties, they can be manipulated through JavaScript. This subtle but powerful feature allows developers to dynamically change the visual interface while enjoying CSS hardware acceleration, and can reduce duplication between front-end code and style sheets.

The following is an example of using custom attributes:

:root {
    --primary-color: papayawhip;
    --base-line-height: 1.4;
}
.thing {
    color: var(--primary-color);
    margin: 0 0 calc(var(--base-line-height) * 1rem);
}

View the demo in Google Chrome (requires chrome version higher than 49)

CSS Mixin and Inheritance

Now, we have variables in our CSS. That's great, but it's not enough to write perfect CSS. What we really need is a way to write reusable CSS. These features already exist in Sass, Less and Stylus, but are not available in regular CSS.

Enter the @apply Rule

Someone at Google is developing a new set of specifications:

This specification defines the @apply rule, which allows developers to store a set of properties in a named variable that can then be referenced in other style rules.

The following is an example of using the @apply rule:

body {
    --alert: {
        color: white;
        padding: 15px;
        margin: 1rem 0;
        border-radius: 6px;
    }
}
.alert-success {
    @apply --alert;
    background-color: olivedrab;
}
.alert-warning {
    @apply --alert;
    background-color: firebrick;
}

At the time of writing this article (April 8, 2016), this feature is still very new and is not supported by Google Chrome or even Chrome Canary, but it is possible in the latest Chromium nightly by enabling the flag.

If you want to try the @apply rule yourself, you can first download the latest Chromium, and then implement @apply by enabling the tag. Here’s how to do it on OS X:

/Applications/Chromium.app/Contents/MacOS/Chromium \  --enable-blink-features=CSSApplyAtRules

To view all the cool styles combined by the above rules, you can refer to my codepen demo:

@apply Codepen demo on Chromium browser

Start writing future CSS now

Once @apply is supported by Chromium and Electron, we will be able to write clean and maintainable styles using native CSS. But until that day comes, we still need to continue to learn preprocessors to fill these gaps.

There are at least two projects that allow you to write the CSS of the future: Myth and cssnext. Of the two projects, cssnext is more active and even has a dedicated git issue to promote the implementation of @apply (Translator's Note: The latest version of postcss-cssnext already supports @apply rules).

The above is the future of CSS.

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