如何在CSS中使导航上方的绿色条浮动

<div class="navbar">
  <ul>
    <li><a href="#">Home</a></li>
    <li><a href="#">About</a></li>
    <li><a href="#">Services</a></li>
    <li><a href="#">Contact</a></li>
  </ul>
  <div class="highlight"></div>
</div>

.navbar {
  position: relative;
  background-color: #f1f1f1;
  height: 50px;
}

.navbar ul {
  list-style-type: none;
  margin: 0;
  padding: 0;
  display: flex;
}

.navbar li {
  margin-right: 10px;
}

.navbar li a {
  display: block;
  padding: 10px;
  text-decoration: none;
  color: #333;
}

.highlight {
  position: absolute;
  top: 0;
  left: 0;
  width: 100px;
  height: 4px;
  background-color: green;
}