chrome/browser/resources/settings/controls/settings_radio_group.html

<style>
  cr-radio-group {
    width: 100%;
  }
</style>
<cr-radio-group selected="[[selected]]"
    on-selected-changed="onSelectedChanged_"
    aria-label$="[[groupAriaLabel]]"
    selectable-elements="[[selectableElements]]">
  <slot></slot>
</cr-radio-group>