[MD History] Color tweaks.

chrome/browser/resources/md_history/synced_device_manager.html

 <link rel="import" href="chrome://resources/html/polymer.html">
 <link rel="import" href="chrome://resources/html/cr/ui/focus_grid.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/iron-list/iron-list.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/paper-button/paper-button.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/paper-item/paper-item.html">
 <link rel="import" href="chrome://resources/cr_elements/cr_lazy_render/cr_lazy_render.html">
 <link rel="import" href="chrome://resources/cr_elements/cr_shared_menu/cr_shared_menu.html">
 <link rel="import" href="chrome://resources/cr_elements/shared_style_css.html">
 <link rel="import" href="chrome://history/shared_style.html">
 <link rel="import" href="chrome://history/synced_device_card.html">
@@ skipping 23 matching lines @@
       #sign-in-guide {
         align-items: center;
         display: flex;
         flex-direction: column;
         justify-content: center;
         overflow-x: hidden;
         text-align: center;
       }
 
       #sign-in-promo {
-        color: var(--primary-text-color);
         font-size: 215%;
         margin-top: 40px;
       }
 
       #sign-in-promo-desc {
-        color: #848484;
+        color: var(--secondary-text-color);
         font-size: 123%;
         margin-top: 10px;
       }
 
       #sign-in-button {
         margin: 24px 0;
         padding-left: 12px;
         padding-right: 12px;
       }
 
@@ skipping 37 matching lines @@
         </paper-item>
         <paper-item id="menuDeleteButton" class="menu-item"
             on-tap="onDeleteSessionTap_">
           $i18n{deleteSession}
         </paper-item>
       </cr-shared-menu>
     </template>
   </template>
   <script src="chrome://history/synced_device_manager.js"></script>
 </dom-module>