index.html

<!DOCTYPE html>
<html>
    <head>
        <!--Meta Tags-->
        <meta charset="utf-8" />
        <title>Dark Mode Demo</title>
        <meta name="description" content="A simple Dark mode switcher" />
        <meta name="viewport" content="width=device-width, initial-scale=1, minimum-scale=1" />

        <!--External Files-->
        <link rel="stylesheet" href="style.css" />
        <script src="script.js" defer></script>
    </head>

    <body>
        <h1><span id="themeName">Light</span> Mode</h1>
        <div id="switchBG" onclick="themeSwitch()">
            <div id="switchFG">
                <img src="images/sun.svg" id="switchIcon" />
            </div>
        </div>

        <div id="description">
            The website defaults to system theme unless you use the button.
        </div>
    </body>
</html>