html,
body {
    margin: 0;
    padding: 0;
    font-family: Arial, Helvetica, sans-serif;
}

:root {
    --bg-word: #5134ff;
}

.container {
    height: 100vh;
    display: flex;
    justify-content: center;
    align-items: center;
}

h1::after {
    content: " HTML CSS";
    color: #fff;
    background: var(--bg-word);

    padding: 10px;
    margin-left: 4px;

    border-radius: 4px;

    animation: 6s swap infinite;
}

@keyframes swap {
    0% {
        content: "singing";
    }

    25% {
        content: "Cats";
    }

    50% {
        content: "Coding";
    }

    75% {
        content: "HTML CSS";
    }

    100% {
        content: "Singing";
    }
}