Fix centering of buttons in pager and dialog.

guacamole/src/main/webapp/styles/ui.css

@@ -225,6 +225,10 @@ div.section {
 
 }
 
+.dialog .footer {
+    text-align: center;
+}
+
 /*
  * List elements
  */
@@ -600,12 +604,7 @@ div#logout-panel {
     background-image: url('../images/action-icons/guac-last-page.png');
 }
 
-#user-list-buttons,
+.buttons,
-#connection-list-buttons {
-    text-align: center;
-    margin: 1em;
-}
-
 .list-pager-buttons {
     text-align: center;
     margin: 1em;