chromium/ash/webui/common/resources/bluetooth/bluetooth_battery_icon_percentage.html

<style include="cr-shared-style">
  :host([is-low-battery_]) #container {
    --iron-icon-fill-color: var(--cros-icon-color-alert);
    color: var(--cros-text-color-alert);
  }

  :host([is-multiple-battery_]) #container {
    padding-end: 6px;
  }

  :host(:not([is-low-battery_])) #container {
    --iron-icon-fill-color: var(--cros-icon-color-secondary);
    color: var(--cros-icon-color-secondary);
  }

  .battery-icon {
    --iron-icon-height: 16px;
    --iron-icon-width: 16px;
    margin-inline-end: -2px;
    padding-bottom: 2px;
  }
</style>
<span id="container">
  <iron-icon id="batteryIcon" class="battery-icon"
      icon="[[getBatteryIcon_(device, batteryType)]]">
  </iron-icon>
  <span id="batteryPercentage">
    [[getBatteryPercentageString_(device, batteryType)]]
  </span>
</span>