button{
            cursor: pointer;
            border: 1px solid #555;
            text-align: center;
            padding: 5px;
            margin-left: 8px;
        }
        .dark{
            background-color: #222;
            color: #e6e6e6;
        }

 <button onclick="myFunction()">تغيير الوضع</button>
     
    <script>
        function myFunction() {
        var element = document.body;
        element.classList.toggle("dark");
        }
    </script>