chromium/ash/webui/common/resources/network/network_config_select.html

<style include="cr-shared-style network-shared md-select">
  .md-select {
    color: var(--cr-primary-text-color);
    width: 100%;
  }

  #outer {
    align-items: stretch;
    display: flex;
    flex-direction: column;
    justify-content: center;
    margin-bottom: var(--cr-form-field-bottom-spacing);
    padding: 0;
  }

  #inner {
    align-items: center;
    display: flex;
    flex-direction: row;
  }

  cr-policy-network-indicator-mojo {
    --cr-tooltip-icon-margin-start: var(--cr-controlled-by-spacing);
  }
</style>

<div id="outer">
  <div id="label" class="cr-form-field-label">[[label]]</div>
  <div id="inner">
    <select class="md-select"
        disabled="[[getDisabled_(disabled, property)]]"
        value="{{value::change}}" aria-label$="[[label]]">
      <template is="dom-repeat" items="[[items]]">
        <option value="[[getItemValue_(item)]]"
            disabled="[[!getItemEnabled_(item, deviceCertsOnly)]]">
          [[getItemLabel_(item, key, oncPrefix)]]
        </option>
      </template>
    </select>
    <cr-policy-network-indicator-mojo
        property="[[property]]" tooltip-position="left">
    </cr-policy-network-indicator-mojo>
  </div>
</div>