Issue #3200868: TOC title shows when TOC is empty

Closes #3200868

css/toc.css

@@ -3,13 +3,18 @@ a.back-to-top {
   font-size: 0.7rem;
   display: none;
 }
+a.back-to-top.is-visible {
+  display: block;
+}
 .toc-js.sticky {
   position: relative;
 }
 .toc-js.sticky.is-sticked {
   position: fixed;
 }
-
 .toc-js {
   display: none;
 }
+.toc-js.is-visible {
+  display: block;
+}