Bug 1918425 - Revert changes to newTabBrowserPanel and sidebar-box z-index r=desktop-theme-reviewers,emilio

This was part of the resolution to Bug 1914938, but hid the search drop down results on new tab.
Once Emilio's patch for Bug 1917458 lands, the original bug will be fixed via a different approach.

Differential Revision: https://phabricator.services.mozilla.com/D222011

browser/themes/shared/browser-shared.css

@@ -476,16 +476,6 @@ toolbarpaletteitem:has(> toolbarbutton.fxms-bmb-button),
        tabs, which is what we explicitly want to avoid doing here. */
     margin-top: var(--bookmarks-toolbar-overlapping-browser-height);
   }
-
-  /* stylelint-disable-next-line media-query-no-invalid */
-  @media (-moz-bool-pref: "sidebar.revamp") {
-    .newTabBrowserPanel,
-    #sidebar-box {
-      /* z-index applied to account for box-shadow cutoff when bookmarks toolbar is present */
-      position: relative;
-      z-index: 1;
-    }
-  }
 }
 
 /* Bookmarks toolbar drop indicator */