Fix misplacement of signin overlay and critical update message banner

chrome/browser/resources/chromeos/quick_unlock/md_pin_keyboard.html

 <!-- TODO(crbug.com/603217): Use i18n instead of string literals. Figure out
                              what i18n to use for keypad, ie, does 1 ABC make
                              sense in every scenario? -->
 
 <link rel="import" href="chrome://resources/cr_elements/icons.html">
 <link rel="import" href="chrome://resources/cr_elements/shared_vars_css.html">
 <link rel="import" href="chrome://resources/html/i18n_behavior.html">
 <link rel="import" href="chrome://resources/html/polymer.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">
@@ skipping 92 matching lines @@
 
       .digit-button.backspace-button {
         color: #FFF;
         left: 0;
         padding: 14px;
         position: absolute;
         top: 0;
       }
 
       .digit-button.backspace-button:not([has-content]) {
-        color: #000;
-        opacity: 0.26;
+        opacity: 0.34;
       }
 
       .digit-button inner-text {
         display: flex;
         flex-direction: column;
         font-family: 'Roboto';
       }
 
       .number {
         color: #FFF;
@@ skipping 142 matching lines @@
                 noink>
             </paper-icon-button>
             <paper-ripple>
           </div>
         </div>
       </div>
     </div>
   </template>
   <script src="pin_keyboard.js"></script>
 </dom-module>