[Glitch] Fix messed up z-index when NoScript blocks media/previews

Port f53bd1bef6 to glitch-soc

Signed-off-by: Thibaut Girka <thib@sitedethib.com>

app/javascript/flavours/glitch/styles/basics.scss

@@ -150,3 +150,15 @@ button {
     height: 100%;
   }
 }
+
+// NoScript adds a __ns__pop2top class to the full ancestry of blocked elements,
+// to set the z-index to a high value, which messes with modals and dropdowns.
+// Blocked elements can in theory only be media and frames/embeds, so they
+// should only appear in statuses, under divs and articles.
+body,
+div,
+article {
+  .__ns__pop2top {
+    z-index: unset !important;
+  }
+}