extra.css: set custom color for superfences tabs

docs/css/extra.css

@@ -8,6 +8,10 @@
  color: #ffab40;
 }
 
+.md-typeset .superfences-tabs > label:hover {
+ color: #ffab40 !important;
+}
+
 code,
 .codehilite pre {
   font-weight: bold;