MD Settings: Update spell check section to spec

chrome/browser/resources/settings/settings_shared_css.html

 <link rel="import" href="/settings_root_css.html">
 
 <!-- Common styles for Material Design settings. -->
 <dom-module id="settings-shared">
   <template>
     <style>
       h2 {
         align-items: center;
         display: flex;
         font-size: 100%;
@@ skipping 186 matching lines @@
       .list-item > .middle {
         flex: 1;
         margin: 8px 16px;
       }
 
       /* The start (left in LTR) part (horizontally) of a list item. */
       .list-item > .start {
         flex: 1;
       }
 
+      .list-item > label span[disabled] {
+        opacity: .65;  /* TODO(michaelpg): check this value with bettes. */
+      }
+
       .list-item > paper-icon-item {
         padding: 0;
       }
 
       /* This button has no ink ripple. */
       .list-item.list-button {
         align-items: center;
         color: var(--google-blue-500);
         font-weight: 500;
       }
@@ skipping 90 matching lines @@
 
       .favicon-image {
         background-repeat: no-repeat;
         background-size: contain;
         height: 16px;
         width: 16px;
       }
     </style>
   </template>
 </dom-module>