dropdown.html

<label>
   <span id="select-label">Favorite animal</span>
   <input type="hidden" name="animal" />
</label>
<button 
   aria-labelledby="select-label select-placeholder"
   aria-controls="select-dropdown"
   aria-haspopup="list"
   aria-expanded="false"
>
  <span id="select-placeholder">Select an option</span>
  <svg aria-hidden><title>Arrow down</title></svg>
</button>
<ul id="select-dropdown" 
    aria-labelledby="select-label"
    aria-hidden
    role="listbox"
>
  <li>Elephant</li>
  <li>Bear</li>
  <li>Lion</li>
</ul>