perf(css): bucket .pagination universal * subject by child tag (#3079)

* Initial plan

* perf(pagination): bucket .pagination universal `*` subject by child tag

---------

Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>

Author: Copilot

.changeset/pagination-universal-subject-perf.md

@@ -0,0 +1,5 @@
+---
+"@primer/css": patch
+---
+
+Replace the universal `*` subject in the `.pagination` responsive rules with tag-bucketed selectors (`> a, > span, > em`). A universal subject compound (`.pagination > *`) forces Blink to test the rule against every direct child on every style recalc; bucketing by the actual child tags lets the engine fast-reject it, reducing wasted selector-matching time without changing the rendered output.

src/pagination/pagination.scss

@@ -109,7 +109,11 @@
   // Responsive
 
   // Hide everything by default
-  > * {
+  // Bucket on the child tag (a/span/em) instead of a universal `*` subject so
+  // Blink can fast-reject this rule during style recalc.
+  > a,
+  > span,
+  > em {
     display: none;
   }
 
@@ -139,7 +143,9 @@
   // Show everything
 
   @include breakpoint(md) {
-    > * {
+    > a,
+    > span,
+    > em {
       display: inline-block;
     }
   }