🚀 CSS Breakthrough: First Public Working Draft of CSS Functions and Mixins Module Published

May 19, 2025

The CSS Working Group has just taken a bold step forward in making CSS more powerful, dynamic, and developer-friendly. On [date], they released the First Public Working Draft of the CSS Functions and Mixins Module — a major milestone that opens the door to more programmable and reusable styles in native CSS.

🔍 What’s in the Draft?

This new module introduces two highly anticipated features:

1. Custom CSS Functions

Authors can now define custom functions in CSS. Think of these as parameterized custom properties — but with significantly more flexibility. These functions can:

Accept parameters like numbers, colors, strings, or even entire style fragments.
Return computed values.
Be used wherever regular CSS values are expected.
Leverage the full power of CSS values and conditional logic.

This means you can create reusable, dynamic logic directly in your stylesheets — no preprocessor needed.

2. Rule Mixins (Early Form)

In addition to functions, the draft also outlines an early implementation of CSS rule mixins. This feature allows authors to define reusable blocks of CSS rules that can be parametrized and inserted into other style rules. It’s a bit like @mixin in Sass, but natively supported in the browser.

Mixins will:

Enable substitution of full property blocks.
Allow conditional and parameterized use.
Reduce repetition and promote maintainable code.

🌐 Why It Matters

Until now, achieving this kind of reusability required preprocessors like Sass, Less, or Stylus. But with native CSS Functions and Mixins:

You get better performance and interoperability.
No build tools or compilation step is required.
Styles become easier to maintain, share, and scale.

This draft is a huge leap toward making CSS a more expressive and powerful language for modern UI development.

🧪 Still Experimental

It’s important to remember this is just a First Public Working Draft. The syntax, behavior, and browser support are all subject to change. But the direction is clear — and it’s exciting.

👀 Stay Tuned

As the spec evolves and browser implementations begin, we’ll keep you updated. For now, it’s a great time to start imagining what’s possible when CSS becomes truly dynamic — all by itself.

The CSS Working Group has published a First Public Working Draft of CSS Functions and Mixins Module. This module defines the ability for authors to define custom functions, acting similar to parametrized custom properties. They can use the full power of CSS’s values and conditional rules. It also defines an early form of a similar idea for CSS rule mixins, allowing parametrized substitution of entire blocks of properties into other rules.