refactor: tooltip was still covered -> z-index: 100 (#30)

Author: ijsnow

src/HoverOverlay.scss

@@ -5,7 +5,7 @@
     display: flex;
     flex-direction: column;
     align-items: stretch;
-    z-index: 20;
+    z-index: 100;
 
     transition: opacity 200ms ease-in-out;