[MD settings] set margins on change download location button

chrome/browser/resources/settings/settings_vars_css.html

 <link rel="import" href="chrome://resources/cr_elements/shared_vars_css.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/paper-styles/color.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/paper-styles/default-theme.html">
 
 <!-- Common css variables for Material Design settings. -->
 <style is="custom-style">
   /* We keep our vars in sort order, though some vars must be defined prior to
    * others. The --settings-* vars are defined explicitly prior to the --paper-*
    * and --iron-* vars.
    */
   :root {
     /* Some colors use non-MD colors.  These custom colors are specified by
      * UX design (bettes@). */
 
     --settings-actionable: var(--cr-actionable);
+    --settings-button-edge-spacing: 12px;
 
     --settings-box-row-padding: 20px;
     --settings-box-row-indent: calc(
         var(--settings-box-row-padding) + var(--settings-indent-width));
     --settings-indent-width: 40px;
     --settings-card-max-width: 680px;
     --settings-disabled-opacity: .65;
     --settings-error-color: var(--paper-red-700);
 
     --settings-list-frame-padding: {
@@ skipping 112 matching lines @@
     --paper-toggle-button-unchecked-button: var(--settings-toggle-button-size);
     --paper-toggle-button-unchecked-ink: var(--settings-toggle-ink-size);
 
     --settings-input-underline: {
       border-color: var(--paper-grey-300);
     };
 
     --paper-input-container-underline: var(--settings-input-underline);
   }
 </style>