<ul class="vertical-header">
  <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>

.vertical-header {
  background-color: #333;
  height: 50px;
  width: 100%;
  display: flex;
  justify-content: center;
  align-items: center;
}

.vertical-header li {
  display: inline-block;
  margin: 0 10px;
}

.vertical-header li a {
  color: #fff;
  text-decoration: none;
}

.vertical-header li a:hover {
  color: #ff0000;
}

<ul class="horizontal-header">
  <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>

.horizontal-header {
  background-color: #333;
  height: 100%;
  width: 200px;
  display: flex;
  flex-direction: column;
  justify-content: center;
  align-items: center;
}

.horizontal-header li {
  margin: 10px 0;
}

.horizontal-header li a {
  color: #fff;
  text-decoration: none;
}

.horizontal-header li a:hover {
  color: #ff0000;
}