MD Settings: Fix minor vertical jumps in animations

chrome/browser/resources/settings/settings_page/settings_subpage.html

 <link rel="import" href="chrome://resources/html/polymer.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/iron-icons/iron-icons.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/iron-resizable-behavior/iron-resizable-behavior.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/neon-animation/neon-animatable-behavior.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/paper-icon-button/paper-icon-button.html">
 <link rel="import" href="chrome://md-settings/settings_shared_css.html">
 
 <dom-module id="settings-subpage">
   <template>
     <style include="settings-shared">
       :host {
         display: block;
-        margin: 8px 0 16px 0;
+      }
+
+      .settings-box.first {
+        padding-bottom: 16px;
+        padding-top: 8px;
       }
 
       paper-icon-button {
         /* The inner icon is 20px in size. paper-icon-button has 8px padding. */
         height: 36px;
         /* Centers the ripple on the icon with appropriate margin on right. */
         margin: 0 12px 0 -8px;
         width: 36px;
       }
 
       h2 {
         color: var(--settings-nav-grey);
         font-size: 107.6923%; /* go to 14px from 13px */
       }
     </style>
     <div class="settings-box first">
       <paper-icon-button icon="arrow-back" on-tap="onTapBack_">
       </paper-icon-button>
       <h2>[[pageTitle]]</h2>
     </div>
     <content></content>
   </template>
   <script src="settings_subpage.js"></script>
 </dom-module>