[MD settings] change settings card width to 640

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;
+        max-width: 640px;
+        min-width: 550px;
         position: relative;
         width: 96%;
       }
 
       :host(.showing-subpage) {
         /* Set the height to the container height so the subpage scrolls. */
         height: 100%;
       }
 
       :host > div {
@@ skipping 14 matching lines @@
 
       .expanding,
       .collapsing {
         /* Must be lower than the cr-toolbar's z-index.
          * See settings_ui.html. */
         z-index: 1;
       }
     </style>
   </template>
 </dom-module>