html {
    font-size: 10px;
}

#central {
    font-size: 30rem;
    background: radial-gradient(rgb(255, 249, 136), rgb(255, 240, 28), rgb(255, 149, 0), rgb(255, 81, 0), rgb(216, 4, 4));
    background-repeat: no-repeat;
    background-position: center;
    background-size: cover;
    border-radius: 50%;
}

a:hover {
    border: solid 15px black;
}