CSS at Scale With StyleX

Build a large enough website with a large enough codebase, and you’ll eventually find that CSS presents challenges at scale. It’s no different at Meta, which is why we open-sourced StyleX, a solution for CSS at scale. StyleX combines the ergonomics of CSS-in-JS with the performance of static CSS. It allows atomic styling of components […]

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Chris WiltzMeta Engineering

·January 12, 2026·Culture

StyleX: Meta’s Answer to CSS at Scale

Large codebases eventually hit CSS roadblocks, a reality Meta knows well. That challenge led to StyleX, an open-source solution pairing CSS-in-JS ergonomics with static CSS performance. The library enables atomic component styling, strips out duplicate definitions to shrink bundles, and keeps the developer API simple.

StyleX is now the standard styling system across Meta properties like Facebook, Instagram, WhatsApp, Messenger, and Threads. External engineering teams at companies such as Figma and Snowflake have also adopted it.

The latest Meta Tech Podcast episode dives into the project with Melissa, a Meta engineer and StyleX maintainer. Pascal Hartig interviews her about the library’s origins, the impact of open source on its growth, and what it’s like supporting large industry adopters.

The episode is available on Spotify, Apple Podcasts, Pocket Casts, and wherever you get your podcasts.

More from the Source

StyleX combines the best of both styling worlds for scalable development.
Meta’s podcast series highlights engineering work from low-level frameworks to user-facing features.
Feedback on the show is welcome via Instagram, Threads, or X.
Career opportunities are listed on the Meta Careers page.

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Written by

Chris Wiltz

Meta Engineering

Writes for Meta Engineering. Part of the Tech Report engineering index.

All articles by Chris Wiltz →