MD Settings: fix overflow scrolling for <settings-dialog>

chrome/browser/resources/settings/bluetooth_page/bluetooth_device_dialog.html

 <link rel="import" href="chrome://resources/html/cr.html">
 <link rel="import" href="chrome://resources/html/polymer.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/iron-flex-layout/classes/iron-flex-layout.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/iron-selector/iron-selector.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/paper-button/paper-button.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/paper-icon-button/paper-icon-button.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/paper-input/paper-input.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/paper-spinner/paper-spinner.html">
 <link rel="import" href="chrome://md-settings/bluetooth_page/bluetooth_device_list_item.html">
 <link rel="import" href="chrome://md-settings/icons.html">
@@ skipping 120 matching lines @@
                 </span>
               </template>
               <span class$="[[getPinClass_(pairingEvent, -1)]]"
                   hidden="[[showAcceptReject_(pairingEvent)]]">
                 $i18n{bluetoothEnterKey}
               </span>
             </div>
           </div>
         </template>
       </div>
-      <div class="button-container">
+      <div class="buttons">
         <template is="dom-if" if="[[isDialogType_(dialogType, 'addDevice')]]">
           <div id="scanning" class="layout horizontal center flex"
               hidden$="[[!adapterState.discovering]]">
             <paper-spinner active="[[adapterState.discovering]]">
             </paper-spinner>
             <span>$i18n{bluetoothScanning}</span>
           </div>
           <paper-button class="end-justified" on-tap="onCancelTap_">
             $i18n{cancel}
           </paper-button>
@@ skipping 10 matching lines @@
           <paper-button hidden$="[[showDismiss_(pairingDevice, pairingEvent)]]"
               on-tap="onCancelTap_">
             $i18n{cancel}
           </paper-button>
         </template>
       </div>
     </settings-dialog>
   </template>
   <script src="chrome://md-settings/bluetooth_page/bluetooth_device_dialog.js"></script>
 </dom-module>