chromium/chrome/browser/resources/chromeos/edu_coexistence/edu_coexistence_button.html

<style>
  cr-button {
    border: 0;
    border-radius: 20px;
  }
</style>
<cr-button class$="[[buttonClasses]]" on-click="onClick"
    disabled="[[disabled]]">
  <template is="dom-if" if="[[hasIconBeforeText(buttonType)]]">
    <iron-icon icon="[[getIcon(buttonType)]]"></iron-icon>
  </template>
  [[getDisplayName(buttonType)]]
</cr-button>