MD Settings: make the background color of the collapsed nav drawer white

chrome/browser/resources/settings/settings_ui/settings_ui.html

 <link rel="import" href="chrome://resources/html/polymer.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/paper-drawer-panel/paper-drawer-panel.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/paper-header-panel/paper-header-panel.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/paper-icon-button/paper-icon-button.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/paper-input/paper-input.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/paper-toolbar/paper-toolbar.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/iron-flex-layout/classes/iron-flex-layout.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/iron-icon/iron-icon.html">
 <link rel="import" href="chrome://md-settings/direction_delegate.html">
 <link rel="import" href="chrome://md-settings/i18n_setup.html">
 <link rel="import" href="chrome://md-settings/icons.html">
 <link rel="import" href="chrome://md-settings/settings_main/settings_main.html">
 <link rel="import" href="chrome://md-settings/settings_menu/settings_menu.html">
 <link rel="import" href="chrome://md-settings/settings_page/settings_router.html">
 <link rel="import" href="chrome://md-settings/settings_shared_css.html">
 
 <dom-module id="settings-ui">
   <template>
     <style include="settings-shared">
       :host {
         @apply(--layout-vertical);
         @apply(--layout-fit);
         -webkit-user-select: none;
         background-color: var(--settings-background-color);
       }
 
       paper-drawer-panel {
         @apply(--layout-center);
-        --paper-drawer-panel-left-drawer-container: {
-          background-color: var(--settings-background-color);
-        };
-        --paper-drawer-panel-right-drawer-container: {
-          background-color: var(--settings-background-color);
+        --paper-drawer-panel-drawer-container: {
+          background: none;  /* Remove default background styling. */
         };
         position: relative;
       }
 
+      #drawer {
+        /* Explicitly set this so that transitions work and look good. */
+        background-color: var(--settings-background-color);
+      }
+
+      #drawer,
+      #drawer .toolbar {
+        transition: background-color .3s, color .3s;
+      }
+
+      :host(:not(.narrowing)) [narrow] #drawer,
+      :host(:not(.narrowing)) [narrow] #drawer .toolbar {
+        background-color: white;
+        transition: none;  /* Transition only when removing [narrow]. */
+      }
+
+      :host(:not(.narrowing)) [narrow] #drawer .toolbar {
+        color: black;
+      }
+
       paper-icon-button {
         --iron-icon-fill-color: var(--settings-title-bar-color);
       }
 
       paper-icon-button[suffix] {
         --iron-icon-fill-color: var(--settings-title-search-color);
         height: 32px; /* After padding, the icon size is 16px. */
         width: 32px;
       }
 
@@ skipping 35 matching lines @@
         --paper-toolbar-content: {
           font-size: 123.08%; /* go to 16px from 13px */
         }
         --paper-toolbar: {
           background-color: var(--settings-title-bar-background-color);
         };
       }
 
       /* Prevent paper-toolbar from setting the margin-right to 24px. */
       paper-icon-button#menu-button {
-        /*
-         * TODO(dschuyler): this margin is on the right regardless of language
-         * direction (e.g. rtl). Make a patch for paper-toolbar in Polymer.
-         */
+        flex-shrink: 0;
+        /* TODO(dschuyler): this margin is on the right regardless of language
+         * direction (e.g. rtl). Make a patch for paper-toolbar in Polymer. */
         margin-right: 0;
       }
 
       .heading {
         -webkit-margin-start: 8px;
       }
 
       paper-drawer-panel:not([narrow]) #main-title {
         display: none;
       }
 
       paper-icon-button[toggles]:not([active]) + #search-input {
         display: none;
       }
 
       .last {
         display: flex;
         justify-content: flex-end;
         width: 100%;
       }
     </style>
     <settings-router current-route="{{currentRoute}}"
         current-route-titles="{{currentRouteTitles}}">
     </settings-router>
     <paper-drawer-panel drawer-width="256px" id="panel" narrow="{{isNarrow_}}"
         responsive-width="900px">
-      <paper-header-panel drawer>
+      <paper-header-panel drawer id="drawer">
         <paper-toolbar class="toolbar">
           <div class="heading flex">$i18n{settings}</div>
         </paper-toolbar>
         <settings-menu current-route="{{currentRoute}}">
         </settings-menu>
       </paper-header-panel>
       <paper-header-panel main>
         <paper-toolbar class="toolbar">
           <paper-icon-button icon="menu" id="menu-button" paper-drawer-toggle>
           </paper-icon-button>
@@ skipping 11 matching lines @@
             </paper-input>
           </div>
         </paper-toolbar>
         <settings-main prefs="{{prefs}}" current-route="{{currentRoute}}">
         </paper-icon-button>
       </paper-header-panel>
     </paper-drawer-panel>
   </template>
   <script src="settings_ui.js"></script>
 </dom-module>