succd: Only show voltage on hover

Another HP HMI thing: "Only show information that is immediately
relevant".  Let's hide the pirani voltage as it is mostly no longer
interesting to the user.  For situations where it is, it can be revealed
by hovering over the pirani pressure value.

succbone/succd/index.html

@@ -70,6 +70,13 @@ td > span {
     row-gap: 2em;
 }
 
+.has-hidden .hidden-text {
+    display: none;
+}
+
+.has-hidden:hover .hidden-text {
+    display: block;
+
 @media only screen and (max-width: 700px) {
     body {
         font-size: 6px;
@@ -115,13 +122,13 @@ td > span {
 
     <table>
         <tr>
-            <th rowspan="2">Pirani Gauge</th>
-            <th>Voltage</th>
-            <td id="volts">{{ .Pirani.Volts }}</td>
-        </tr>
-        <tr>
-            <th>Pressure</th>
-            <td id="mbar">{{ .Pirani.Mbar }}</td>
+            <th>Pirani Pressure</th>
+            <td class="has-hidden">
+                <div id="mbar">{{ .Pirani.Mbar }}</div>
+                <div class="hidden-text" style="color: #606060;">
+                    <span>Voltage: </span><span id="volts">{{ .Pirani.Volts }}</span>
+                </div>
+            </td>
         </tr>
     </table>