What changed

GitHub recently dropped the CSS module file prefix from its class names. Selectors like [class^="Diff-module__diffTargetable"] no longer match, because the same element is now diffTargetable__<hash>:

• Before: <file>-module__<name>__<hash>
• Now: <name>__<hash>

Class names that come from Primer (prc-…) are unchanged. Many selectors across the extension broke at once, so this issue tracks the whole cleanup.

How to fix a selector

• Replace the Foo-module__bar prefix match with a contains match on the bare name: [class*="bar"]. Don't use ^=, the order of classes on an element isn't stable.
• The bare name is generic and can match elsewhere on the page. Always scope it to a stable ancestor (data-testid, aria-label, prc-…, or another already-matched element) and check that it doesn't match unrelated elements.
• Prefer data-testid, aria-* or prc-… hooks whenever the element has one.