<nav>
  <ul class="main-menu">
    <li>Home</li>
    <li>About</li>
    <li>
      Services
      <ul class="sub-menu">
        <li>Web Design</li>
        <li>SEO</li>
        <li>Content Creation</li>
      </ul>
    </li>
    <li>Contact</li>
  </ul>
</nav>

.main-menu > li:has(.sub-menu):before {
  content: "▼";
  margin-left: 5px;
  font-size: 0.75em;
}