WebUI: Only highlight scrollable divs

chrome/browser/resources/settings/settings_shared_css.html

 <link rel="import" href="chrome://resources/cr_elements/shared_style_css.html">
 <link rel="import" href="settings_vars_css.html">
 
 <!-- Common styles for Material Design settings. -->
 <dom-module id="settings-shared">
   <template>
     <style include="cr-shared-style">
       :host-context([dir=rtl]) button[is='paper-icon-button-light'] {
         transform: scaleX(-1);  /* Flip on the X axis (aka mirror). */
       }
@@ skipping 296 matching lines @@
         flex-direction: row;
         max-width: 100%;
         min-width: 0;  /* Workaround for text elision in sub-elements. */
       }
 
       /* Expand to fill-up available space. */
       .settings-row.wide {
         flex: 1;
       }
 
-      .no-outline,
-      [scrollable] .no-outline {
+      .no-outline {
         background: none;
         outline: none;
       }
 
       /* Helper for a list frame to automatically avoid the separator line. */
       .vertical-list > *:not(:first-of-type) {
         border-top: var(--settings-separator-line);
       }
 
       /* The separator a vertical line like a horizontal rule <hr> tag, but goes
@@ skipping 63 matching lines @@
         transform: rotate(-135deg);
       }
 
       .column-header {
         color: var(--paper-grey-600);
         font-weight: 500;
       }
     </style>
   </template>
 </dom-module>