[MD settings] css for row separator

chrome/browser/resources/settings/default_browser_page/default_browser_page.html

 <link rel="import" href="chrome://resources/html/polymer.html">
 <link rel="import" href="chrome://resources/html/web_ui_listener_behavior.html">
 <link rel="import" href="default_browser_browser_proxy.html">
 <link rel="import" href="../icons.html">
 <link rel="import" href="../settings_shared_css.html">
 
 <dom-module id="settings-default-browser-page">
   <template>
     <style include="settings-shared">
     </style>
     <template is="dom-if" if="[[maySetDefaultBrowser_]]">
       <div class="settings-box first two-line">
         <div class="start">
           <div id="canBeDefaultBrowser">$i18n{defaultBrowser}</div>
           <div class="secondary">$i18n{defaultBrowserMakeDefault}</div>
         </div>
-        <div class="secondary-action">
-          <paper-button class="secondary-button"
-              on-tap="onSetDefaultBrowserTap_">
-            $i18n{defaultBrowserMakeDefaultButton}
-          </paper-button>
-        </div>
+        <div class="separator"></div>
+        <paper-button class="secondary-button"
+            on-tap="onSetDefaultBrowserTap_">
+          $i18n{defaultBrowserMakeDefaultButton}
+        </paper-button>
       </div>
     </template>
     <template is="dom-if" if="[[!maySetDefaultBrowser_]]">
       <div class="settings-box first">
         <div class="start" hidden$="[[!isDefault_]]" id="isDefault">
           $i18n{defaultBrowserDefault}
         </div>
         <div class="start" hidden$="[[!isSecondaryInstall_]]"
             id="isSecondaryInstall">
           $i18n{defaultBrowserSecondary}
         </div>
         <div class="start" hidden$="[[!isUnknownError_]]" id="isUnknownError">
           $i18n{defaultBrowserError}
         </div>
       </div>
     </template>
   </template>
   <script src="default_browser_page.js"></script>
 </dom-module>