[Web] Minor UI Fix

fixes column overflowing issues in small-screen devices.

data/web/css/mailbox.css

@@ -8,13 +8,8 @@ table.footable>tbody>tr.footable-empty>td {
 .panel panel-default {
   overflow: visible !important;
 }
-.table-responsive {
-  overflow: visible !important;
-}
-@media screen and (max-width: 767px) {
-  .table-responsive {
-    overflow-x: scroll !important;
-  }
+.btn-group {
+  width: max-content;
 }
 .footer-add-item {
   display:block;
@@ -45,4 +40,4 @@ table.footable>tbody>tr.footable-empty>td {
 }
 .table-lines {
   vertical-align: inherit;
-}
+}