anime.html

<!doctype  html>
<html lang="ja">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>ブラウザのタブに表示されるタイトル</title>
    <style>
        html {
            height: 100%;
            overflow: hidden;
        }

        body {
            background-color: black;
            color: skyblue;
            font-size: 3rem;
            display: grid;
            place-items: center;
            height: 100%;
            animation-name: rotation;
            animation-iteration-count: infinite;
            animation-duration: 1s;
        }

        @keyframes rotation {
            from {
                transform: rotate(0);
            }

            to {
                transform: rotate(1turn);
            }
        }
    </style>
</head>

<body>
    初めてかもしれないHTML
</body>

</html>