start . me .
Directory path . web , dhtml .

HTML Document File : themes.html

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

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Theme Switcher Example</title>
    <style>
        * {
            background-color: var(--background-color);
            color: var(--foreground-color);
        }

        body {
            font-family: Arial, sans-serif;
        }

        button {
            padding: 10px;
            margin: 5px;
            cursor: pointer;
            border-radius: 25px;
        }

        .theme-light {
            --background-color: #f0f0f0;
            --foreground-color: #333;
        }

        .theme-dark {
            --background-color: #333;
            --foreground-color: #f0f0f0;
        }

        .theme-flame {
            --background-color: orange;
            --foreground-color: red;
        }
    </style>
</head>

<body>
    <script>

        // a theme is saved in localStorage ( or default )
        setTheme(localStorage.getItem('theme') || "light");

        function setTheme(theme) {
            document.body.classList.remove('theme-' + localStorage.getItem('theme'));
            localStorage.setItem('theme', theme);
            document.body.classList.add('theme-' + theme);
        }
    </script>

    <h1>Theme Switcher Example</h1>
    <p>Click the buttons below to switch themes:</p>
    <button onclick="setTheme('light')">Light Theme</button>
    <button onclick="setTheme('dark')">Dark Theme</button>
    <button onclick="setTheme('flame')">Flame Theme</button>

    <hr>
    <script src="https://arkenidar.com/web/show-source.js"></script>
</body>

</html>