chromium/third_party/blink/web_tests/fast/forms/select/select-percent-width.html

<div style="display: table-cell; width: 200px">
    <select style="width: 50%">
        <option>Lorem ipsum dolor sit amet, consectetur adipisicing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua.</option>
    </select>
</div>
<div style="display: table-cell; width: 200px">
    <select style="width: 50%" multiple>
        <option>Lorem ipsum dolor sit amet, consectetur adipisicing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua.</option>
    </select>
</div>