:where() zero specificity

React chapter 118 · Radix Themes · MUI · Tailwind preflight · source: radix-ui/themes · :where() in library defaults

The problem

A library ships .btn { color: blue; font-weight: 800 }. The app writes .btn { color: red }. Equal specificity — source order wins, often the library bundle after yours. Consumers !important their way out.

The pattern that fixes it

:where(.btn) { color: blue } has zero specificity. The consumer .btn { color: red } always wins without !important. Radix Themes and many resets wrap defaults in :where() so they are easy to override.

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