MD Settings: Replace paper-item with button under iron-dropdown, part1.

chrome/browser/resources/settings/settings_shared_css.html

 <link rel="import" href="chrome://resources/cr_elements/shared_style_css.html">
 <link rel="import" href="/settings_root_css.html">
 
 <!-- Common styles for Material Design settings. -->
 <dom-module id="settings-shared">
   <template>
     <style include="cr-shared-style">
       h2 {
         align-items: center;
         display: flex;
@@ skipping 27 matching lines @@
         };
         --paper-input-container-underline: {
           background: var(--paper-grey-300);
         };
       }
 
       paper-dropdown-menu paper-listbox {
         padding: 0;
       }
 
+      iron-dropdown .dropdown-item,
       paper-dropdown-menu .dropdown-item {
         align-items: center;
         background: none;
         border: none;
         color: var(--paper-grey-800);
         display: flex;
         font: inherit;
         min-height: 48px;
         padding: 0 16px;
         text-align: start;
         width: 100%;
       }
 
       paper-dropdown-menu .dropdown-item.iron-selected {
         font-weight: bold;
       }
 
+      iron-dropdown .dropdown-item:focus,
       paper-dropdown-menu .dropdown-item:focus {
         background-color: var(--paper-grey-300);
         outline: none;
       }
 
       iron-dropdown .dropdown-content {
         background-color: white;
         box-shadow: 0 2px 6px var(--paper-grey-500);
       }
 
+      iron-dropdown .dropdown-content .dropdown-item,
       iron-dropdown .dropdown-content paper-item {
         @apply(--settings-actionable);
       }
 
+      iron-dropdown .dropdown-content .dropdown-item:hover,
       iron-dropdown .dropdown-content paper-item:hover {
         background-color: var(--settings-hover-color);
       }
 
       span ~ a {
         -webkit-margin-start: 4px;
       }
 
       [is='action-link'],
       [is='action-link']:active,
@@ skipping 257 matching lines @@
 
       .favicon-image {
         background-repeat: no-repeat;
         background-size: contain;
         height: 16px;
         width: 16px;
       }
     </style>
   </template>
 </dom-module>