index.html

<!DOCTYPE html>
<html lang="en">

  <head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible"
          content="IE=edge">
    <meta name="viewport"
          content="width=device-width, initial-scale=1.0">
    <title>JS Color Flipper | Simple</title>
    <link rel="stylesheet"
          href="style.css">
  </head>

  <body>
    <nav>
      <div class="navbar">
        <div class="title">JS Color Flipper</div>
        <div class="links">
          <ul>
            <li id="simple">simple</li>
            <li id="rgb">rgb</li>
            <li id="hex">hex</li>
          </ul>
        </div>
      </div>
    </nav>
    <section>
      <h1>Background Color: <span id="colorDisplay">green</span></h1>
      <button id="change-color">Change Color</button>
      <script src="script.js"></script>
    </section>
  </body>

</html>