added border on focus of hambuger icon

Created by: TorRydberg

Fixes #30420 (closed)

site/assets/scss/_subnav.scss

@@ -41,4 +41,8 @@
 .bd-search-docs-toggle {
   line-height: 1;
   color: $gray-900;
+
+  &:focus {
+    border: 3px solid $purple-100;
+  }
 }