chromium/ash/webui/common/resources/cr_elements/cr_expand_button/cr_expand_button.html

<style include="cr-actionable-row-style">
  :host([disabled]) {
    opacity: 0.65;
    pointer-events: none;
  }

  :host([disabled]) cr-icon-button {
    display: var(--cr-expand-button-disabled-display, initial);
  }

  #label {
    flex: 1;
    padding: var(--cr-section-vertical-padding) 0;
  }

  cr-icon-button {
    --cr-icon-button-icon-size: var(--cr-expand-button-icon-size, 20px);
    --cr-icon-button-size: var(--cr-expand-button-size, 36px);
  }
</style>

<div id="label" aria-hidden="true"><slot></slot></div>
<cr-icon-button id="icon" aria-labelledby="label" disabled="[[disabled]]"
    tabindex="[[tabIndex]]" part="icon"></cr-icon-button>