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+---
+'@backstage/ui': patch
+---
+
+Fixed CSS Module purity errors for Next.js 16 compatibility
+
+After upgrading to Next.js 16.1.6, the build failed with CSS Module purity errors. Next.js 16 with Turbopack enforces stricter validation requiring global selectors like `[data-theme='dark']` to be combined with local classes.
+
+Changed nested selector structure from `[data-theme='dark'] { .class { } }` to flattened `[data-theme='dark'] .class { }`.
+
+**Affected components:** popover, tooltip