TLDR Tech / DevOps
Improving site performance by shipping more CSS
GitHub migrated github.com from CSS-in-JS to CSS Modules to remove client- and server-side styling overhead at scale. The migration cut Primer server-side rendering time by 55%, reduced component initialization time by 25%, and later improved SSR by up to 22% on some pages while thousands of sx usages were gradually replaced through feature flags, visual regression tests, codemods, and staged rollouts.
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