[MD History] Use proper shadows for cards.

chrome/browser/resources/md_history/synced_device_card.html

 <link rel="import" href="chrome://resources/cr_elements/icons.html">
 <link rel="import" href="chrome://resources/html/polymer.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/paper-styles/shadow.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/iron-collapse/iron-collapse.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/iron-icon/iron-icon.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/iron-flex-layout/iron-flex-layout.html">
 <link rel="import" href="chrome://resources/html/icon.html">
 <link rel="import" href="chrome://history/browser_service.html">
 <link rel="import" href="chrome://history/constants.html">
 <link rel="import" href="chrome://history/searched_label.html">
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       }
 
       #dropdown-indicator {
         -webkit-margin-end: 12px;
         color: var(--secondary-text-color);
         height: 20px;
         width: 20px;
       }
 
       #collapse {
-        border-bottom: 1px solid var(--card-border-color);
         overflow: hidden;
       }
 
       #history-item-container {
+        @apply(--card-box-shadow);
         background: #fff;
-        border: 1px solid var(--card-border-color);
         border-radius: 2px;
       }
 
       #item-container {
         @apply(--layout-center);
         @apply(--layout-horizontal);
         min-height: var(--item-height);
       }
 
       #window-separator {
@@ skipping 30 matching lines @@
           </template>
           <div class="item-container">
             <p on-tap="openAllTabs_" id="open-tabs">$i18n{openAll}</p>
           </div>
         </div>
       </iron-collapse>
     </div>
   </template>
   <script src="chrome://history/synced_device_card.js"></script>
 </dom-module>