index.html

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Jaunimas gali</title>
    <style>
        .my_wrapper {
            height: 100vh;
            display: flex;
            align-items: center;
            text-align: center;
            justify-content: center;
            flex-direction: column;
        }

        .my_button {
            background: #ff3454;
            color: #ffffff;
            padding: 20px 40px;
            font-size: 20px;
            border: 0;
            border-radius: 20px;
            transition: transform .6s;
            margin: 10px;
        }

        .my_button:hover {
            transform: scale(2) rotate(360deg);
        }
    </style>
</head>
<body>
    <div class="my_wrapper">
        <h1>Laba diena</h1>
        <h2>Kaip laikotes?</h2>
        <p>
            <button id="mygtukas" class="my_button">Paspausk mane</button>
        </p>
    </div>

<script>
    let my_button = document.querySelector("#mygtukas");
    let body = document.querySelector("body");

    my_button.addEventListener("click", function() {
        body.style.backgroundColor = '#'+(Math.random()*0xFFFFFF<<0).toString(16);
    });
</script>
</body>
</html>