User-friendly CSS tooltip

pdbfixer/html/addHydrogens.html

@@ -46,6 +46,45 @@ function applyPaddingToWaterBox(padding) {
     }
 }    
 </script>
+<style>
+a.tooltip {
+    display: inline;
+    position: relative;
+    color: #000;
+    border-bottom: 1px dotted #000;
+    text-decoration: none;
+}
+a.tooltip:hover:after {
+    content: attr(rel);
+    text-align: center;
+    font-size: 80%%;
+    background: #000;
+    color: #fff;
+    width: 250px;
+    bottom: 30px;
+    left: -125px;
+    padding: 10px 15px;
+    position: absolute;
+    z-index: 100;
+    /* Effects */
+    background: rgba(0,0,0,0.75);
+    border-radius: 5px;
+    box-shadow: 0 0 25px #333;
+}
+/* Down arrow */
+a.tooltip:hover:before {
+    border: solid;
+    border-color: #333 transparent;
+    border-width: 10px 10px 0 10px;
+    bottom: 20px;
+    left: -6px;
+    content: "";
+    position: absolute;
+    z-index: 99;
+    /* Effects */
+    border-color: rgba(0,0,0,0.75) transparent;
+}
+</style>
 <form id="mainform" method="post" action="/">
 <h1>Delete Heterogens</h1>
 A heterogen is any residue other than a standard amino acid or nucleotide.  Do you want to delete heterogens?
@@ -85,7 +124,7 @@ Add a water box surrounding the model?
                 <option value="truncatedOctahedron">Truncated octahedron</option>
                 <option value="rhombicDodecahedron">Rhombic dodecahedron</option>
             </select>
-            <span title="The specified padding will be applied on the largest molecular axis, maintaining selected geometry" style="border-bottom: 1px dotted black; cursor: help">?</span>
+            <a href="#" rel="The specified padding will be applied on the largest molecular axis, while maintaining selected geometry." class="tooltip">?</a>
         </div>
         </td>
         </tr>