md-settings: Tweak padding for action/cancel buttons and subpage header.

ui/webui/resources/cr_elements/shared_style_css.html

 <link rel="import" href="chrome://resources/html/polymer.html">
 <link rel="import" href="chrome://resources/cr_elements/shared_vars_css.html">
 
 <!-- Common styles for Material Design WebUI. Included directly in
   settings_shared_css.html. -->
 <dom-module id="cr-shared-style">
   <template>
     <style>
       /* Chrome spinners should be blue. */
       paper-spinner {
         --paper-spinner-layer-1-color: var(--google-blue-500);
         --paper-spinner-layer-2-color: var(--google-blue-500);
         --paper-spinner-layer-3-color: var(--google-blue-500);
         --paper-spinner-layer-4-color: var(--google-blue-500);
       }
 
       .action-button {
         background: var(--google-blue-500);
         color: white;
         --paper-button-flat-keyboard-focus: {
           background: rgb(58, 117, 215);  /* 88% of --google-blue-500 */
         };
       }
 
       .action-button[disabled] {
-        opacity: .25;  /* TODO(dbeam): check this value with bettes. */
+        opacity: .2;
       }
 
       .cancel-button {
         --paper-button-flat-keyboard-focus: {
           background: rgba(0, 0, 0, .12);
         };
       }
 
       .action-button,
       .cancel-button {
         font-weight: 500;
+        padding: 0 16px;
       }
 
       [actionable] {
         @apply(--cr-actionable);
       }
 
       button[is='paper-icon-button-light'] {
         @apply(--cr-paper-icon-button-margin);
         background-position: center;
         background-repeat: no-repeat;
@@ skipping 54 matching lines @@
       [selectable]:focus,
       [selectable] > :focus {
         @apply(--cr-selectable-focus);
       }
       [selectable] > * {
         @apply(--cr-actionable);
       }
     </style>
   </template>
 </dom-module>