[MD settings] adjust button layout

ui/webui/resources/cr_elements/shared_vars_css.html

 <link rel="import" href="chrome://resources/html/polymer.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/paper-styles/color.html">
 
 <!-- Common css variables for Material Design WebUI. -->
 <style is="custom-style">
   :root {
     --cr-actionable: {
       cursor: pointer;
     };
 
     /* Spacing between policy (controlledBy) indicator and control. */
     --cr-controlled-by-spacing: 24px;
 
     --cr-focused-item-color: var(--google-grey-300);
 
     /* The inner icon is 20px in size. paper-icon-button has 8px padding. */
     --cr-icon-ripple-size: 36px;
     --cr-icon-ripple-padding: 8px;
 
     --cr-icon-size: 20px;
 
     --cr-icon-height-width: {
       height: var(--cr-icon-size);
       width: var(--cr-icon-size);
     }
 
+    --cr-icon-ripple-margin: calc(var(--cr-icon-ripple-padding) * -1);
+
     --cr-paper-icon-button-margin: {
       /* Shift button so ripple overlaps the end of the row. */
-      -webkit-margin-end: calc(var(--cr-icon-ripple-padding) * -1);
-      -webkit-margin-start: calc(var(--cr-icon-ripple-padding) * -1);
+      -webkit-margin-end: var(--cr-icon-ripple-margin);
+      -webkit-margin-start: var(--cr-icon-ripple-margin);
     }
 
     --cr-selectable-focus: {
       background-color: var(--cr-focused-item-color);
       outline: none;
     }
     --cr-separator-height: 1px;
     --cr-separator-line: var(--cr-separator-height) solid rgba(0, 0, 0, 0.06);
     --paper-checkbox-ink-size: 40px;
   }
 </style>