how to make your own dropdown header in html code example

Example 1: Dropdown menu HTML

<select id="gender">
  <option value="male"> Male </option>
  <option value="female"> Female</option>
  </select>

Example 2: dropdown navigation menu

<nav role="navigation">
  <ul>
    <li><a href="#">One</a></li>
    <li><a href="#">Two</a>
      <ul class="dropdown">
        <li><a href="#">Sub-1</a></li>
        <li><a href="#">Sub-2</a></li>
        <li><a href="#">Sub-3</a></li>
      </ul>
    </li>
    <li><a href="#">Three</a></li>
  </ul>
</nav>