Fix CSS .topbar-items .sub-item class

It needs z-index: 100; or else depending on the screen width the menu
might not be visible (the IOCCC image is over it).

ioccc.css

@@ -612,6 +612,7 @@ transition: all .3s ease;
     text-align: left;
     background-color: whitesmoke;
     left: -100%;
+    z-index:100;
 }
 
 .topbar-items .item:hover .sub-item{