chrome/browser/resources/settings/settings_icons_css.html

<link rel="import" href="chrome://resources/html/polymer.html">

<!-- Common icon classes for Material Design settings page. -->
<dom-module id="settings-icons">
  <template>
    <style>
<if expr="chromeos">
      cr-icon-button.icon-add-circle {
        background-image: url(./images/settings_icon_add_circle.svg);
      }
      cr-icon-button.icon-add-wifi {
        background-image: url(./images/settings_icon_add_wifi.svg);
      }
</if>
    </style>
  </template>
</dom-module>