ナビゲーションバーの「ボタン」を中央に配置するにはどうすればよいですか？

.navbar {
  position: relative;
  margin-top: -47px;
}

.navbar ul {
  width: 99%;
  list-style-type: none;
  margin: auto;
  padding: 0;
  overflow: hidden;
  background-color: rgba(0, 0, 0, 0.5);
}

.navbar li {}

.navbar li a {
  float: left;
  color: white;
  padding: 14px 16px;
  text-decoration: none;
}

li a:hover {
  background-color: rgba(0, 0, 0, 0.8);
}

.dropdown-content {
  display: none;
  position: absolute;
  margin-top: 47px;
  background-color: rgba(0, 0, 0, 0.8);
  text-align: center;
  min-width: 120px;
  box-shadow: 0px 8px 16px 0px rgba(0, 0, 0, 0.2);
  z-index: 1;
}

.dropdown:hover .dropdown-content {
  display: block;
}

.active {
  background-color: rgba(0, 0, 0, 0.8);
  color: white;
}

<div class="navbar">
  <ul>
    <li><a class="active" href="index.html">Home</a></li>
    <li class="dropdown"><a href="bewegingillusie.html">Plans</a>
      <div class="dropdown-content">
        <a href="about_us.html">Route</a>
        <a href="about_the_website.html">Places I want to go</a>
        <a href="about_the_website.html">My budget</a>
      </div>
    </li>
    <li class="dropdown"><a href="fotoillusie.html">Journey</a>
      <div class="dropdown-content">
        <a href="about_us.html">South-Africa</a>
        <a href="about_the_website.html">Thailand</a>
        <a href="about_the_website.html">Country1</a>
        <a href="about_the_website.html">Country2</a>
        <a href="about_the_website.html">Country3</a>
        <a href="about_the_website.html">Country4</a>
      </div>
    </li>
    <li><a href="kleurillusie.html">Photos</a></li>
    <li><a href="vormillusie.html">Other websites</a></li>
    <li class="dropdown"><a href="about.html">About</a></li>
  </ul>
</div>