18F/web-design-standards

<form class="usa-form">
  <label class="usa-label" for="options">Dropdown label</label>
  <select class="usa-select"
    name="options"
    id="options"
    {% if multiple %}multiple{% endif %}
    {% if size %}size="{{ size }}"{% endif %}
    {% if disabled_state == 'disabled' %} disabled {%- endif %}
    {% if disabled_state == 'aria-disabled' %} aria-disabled="true" {%- endif %}  
  >
    <option value>- Select -</option>
    <option value="value1">Option A</option>
    <option value="value2">Option B</option>
    <option value="value3">Option C</option>
  </select>
</form>