Fix theme explorer styling

Author: tcbegley

docs/templates/theme-explorer.html

@@ -51,7 +51,9 @@
   </select>
 </div>
 <main class="dbcd-main mb-2 mx-2 mx-md-4 my-4">
-  <div style="transform:translateZ(0);box-shadow:0 0 2px 1px #9c9c9c;">
+  <div
+    style="transform:translateZ(0);box-shadow:0 0 2px 1px #9c9c9c;height:calc(100vh - 106px)"
+  >
     <iframe
       id="explorer-iframe"
       src="/docs/themes/explorer/bootstrap"