Fix superscripts floating above sticky table headers (#57661)

Author: heiskr

src/frame/components/page-header/Header.module.scss

@@ -6,11 +6,6 @@
   display: unset;
 }
 
-// Need children of portal root to be higher z-index to show dropdown
-.portalRoot * {
-  z-index: 3 !important;
-}
-
 // Contains the logo and version picker and used when the smaller width search
 // input UI is closed.
 .logoWithClosedSearch {

src/frame/components/page-header/Header.tsx

@@ -149,7 +149,7 @@ export const Header = () => {
       {error !== '404' && <HeaderNotifications />}
       <header
         className={cx(
-          'color-bg-default p-2 position-sticky top-0 z-1 border-bottom',
+          'color-bg-default p-2 position-sticky top-0 z-2 border-bottom',
           scroll && 'color-shadow-small',
         )}
         role="banner"

src/frame/components/ui/MarkdownContent/stylesheets/table.scss

@@ -35,6 +35,7 @@
     thead {
       position: sticky;
       top: 105px; // 88 + 8 + 8 + 1, space for the site header
+      z-index: 1; // Ensure header stays above content including superscripts
 
       @include breakpoint-xxl {
         top: 65px !important; // 48 + 8 + 8 + 1, space for the site header

src/frame/stylesheets/dialog-overrides.scss

@@ -10,3 +10,8 @@
     visibility: hidden !important;
   }
 }
+
+// Fix z-index for ActionMenu overlays (version picker, etc.) to appear above site header
+#__primerPortalRoot__ * {
+  z-index: 3 !important;
+}