Move settings-section animations into setting-section, make better

chrome/browser/resources/settings/settings_page_css.html

 <link rel="import" href="chrome://resources/html/polymer.html">
 <link rel="import" href="/settings_page/main_page_behavior.html">
 
 <dom-module id="settings-page-styles">
   <template>
     <style>
       :host {
         box-sizing: border-box;
         display: block;
         height: inherit;
         margin: 0 auto;
         max-width: 960px;
         min-width: 622px;
         position: relative;
         width: 96%;
       }
 
+      :host(.showing-subpage) {
+        /* Set the height to the container height so the subpage scrolls. */
+        height: 100%;
+      }
+
       :host > div {
         height: inherit;
       }
 
       :host > div > :not(.expanded) {
         /* The margin and padding here are doing two things: make the total
          * separation 24px; and make scrollIntoView align the section header
          * with the top item in the side nav menu. Both things are desired
          * by Alan (bettes@). */
         margin-bottom: 3px;
       }
 
-      .expanded {
+      settings-section.expanded {
         min-height: 100%;
       }
 
-      .expanding,
-      .collapsing {
+      settings-section.expanding,
+      settings-section.collapsing {

[Dan Beam, 2016/08/05 00:47:07]

why are you adding this?  i had to remove a tag names recently because they
weren't helpful.  for specificity?  if so: which rule?

         /* Must be lower than the paper-header-panel's z-index.
          * See settings_ui.html. */
         z-index: 1;
       }
     </style>
   </template>
 </dom-module>