 <select multiple="multiple" class="multiple-select">
        <optgroup label="Group 1">
          <option value="1">Option 1</option>
          <option value="2">Option 2</option>
          <option value="3">Option 3</option>
        </optgroup>
        <optgroup label="Group 2">
          <option value="4">Option 4</option>
          <option value="5">Option 5</option>
          <option value="6">Option 6</option>
        </optgroup>
        <optgroup label="Group 3">
          <option value="7">Option 7<