NightMode/index.html

<!DOCTYPE html>
<html>

<head>
    <title>Dark Mode Toggle</title>
    <meta name="viewport" content="width=device-width, initial-scale=1">
    <link rel="stylesheet" href="app.css">
    <style>
        body {
            background-color: #f6f6f6;
            transition: background-color .3s;
        }

        body[light-mode=dark] {
            background-color: #141516;
            color: #ced4e2;
        }

        body[light-mode="dark"] .light-mode-button span:nth-child(1) {
            background-color: #ced4e2;
            color: #141516;
        }

        body[light-mode=dark] .light-mode-button span:nth-child(2) {
            left: 65px;
            background-color: #141516;
        }

        /* Light Mode Button Styles
        --------------------------- */
        .light-mode-button {
            background: 0;
            border: 0;
            box-sizing: border-box;
            cursor: pointer;
            height: 40px;
            width: 100px;
            position: relative;
            border: 1px solid rgba(255, 255, 255, 0);
        }

        .light-mode-button:focus {
            outline: none;
            /* Not ideal for accessibility */
        }

        .light-mode-button span:nth-child(1) {
            position: absolute;
            top: 0;
            left: 0;
            width: 100px;
            height: 40px;
            border-radius: 20px;
            background-color: #d6d7db;
            box-shadow: inset 1px 1px 3px 0 rgb(0 0 0 / 40%);
            transition: .3s;
        }

        .light-mode-button span:nth-child(2) {
            position: absolute;
            top: 5px;
            left: 5px;
            width: 30px;
            height: 30px;
            background-color: #fff;
            border-radius: 50%;
            box-shadow: 1px 1px 2px 0 rgb(0 0 0 / 40%);
            transition: .3s;


        }
    </style>
</head>

<body>
    <script>
        window.addEventListener("storage", function () {
            if (localStorage.lightMode == "dark") {
                app.setAttribute("light-mode", "dark");
            } else {
                app.setAttribute("light-mode", "light");
            }
        }, false);
        var app = document.getElementsByTagName("BODY")[0];
        if (localStorage.lightMode == "dark") {
            app.setAttribute("light-mode", "dark");
        }
    </script>
    <div class="container">
        <h1>Dark Mode Toggle</h1>
        <button class="light-mode-button" aria-label="Toggle Light Mode" onclick="toggle_light_mode()">
            <span></span>
            <span></span>
        </button>
    </div>
    <script>
        function toggle_light_mode() {
            var app = document.getElementsByTagName("BODY")[0];
            if (localStorage.lightMode == "dark") {
                localStorage.lightMode = "light";
                app.setAttribute("light-mode", "light");
            } else {
                localStorage.lightMode = "dark";
                app.setAttribute("light-mode", "dark");
            }
        }
    </script>
</body>

</html>