JSFiddle - React, Tailwind, and code Playground

HTML

<div class="main-navigation">
  <ul>
    <li>item1</li>
    <li>item2</li>
    <li>item3</li>
    <li>item4</li>
    <li>item5</li>
  </ul>
</div>

CSS

* {
  margin: 0;
  padding: 0;
} /* 仮のコードです */

.main-navigation {
  /* width: 100vw; */
  position: fixed;
  left: 0;
  right: 0;
  bottom: 0;
  background-color: gray; /* 要素の可視化 */
}

.main-navigation ul {
  text-align: center;
}

.main-navigation li {
  display: inline-block;
  margin-right: 20px;
}