index.html

<!DOCTYPE html>
<html>
<head>
	<title>Curso JS</title>
	<meta charset="utf-8">
		<link rel="stylesheet" type="text/css" href="background.css">
	<link rel="preconnect" href="https://fonts.googleapis.com">
<link rel="preconnect" href="https://fonts.gstatic.com" crossorigin>
<link href="https://fonts.googleapis.com/css2?family=Roboto:ital,wght@1,300&display=swap" rel="stylesheet">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<script src="https://kit.fontawesome.com/2e3d4c9f14.js" crossorigin="anonymous"></script>
</head>
<body>
	<nav>
        <div class="nav-center">
            <h4>Color Flipped</h4>
            <ul class="nav-link">
                <li><a href="index.html">Hexadecimal</a></li>
                <li><a href="hex.html">Simple</a></li>
            </ul>
        </div>
    </nav>
    <main>
        <div class="main">
            <h2>Background Color: <span class="color">#f1f5f8</span></h2>
        </div>
        
    </main>

    <button id="button">Click Aquí</button>
<script src="https://cdn.jsdelivr.net/npm/axios/dist/axios.min.js"></script>
<script src="background1.js"></script>
</body>
</html>