html,
body {
    height: 100%;
}
body {
    margin: 0;
    background: #000;
}
body {
    height: 100%;
    display: flex;
    flex-direction: column;
    justify-content: center;
    align-items: center;
}
.container {
    text-align: center;
    max-width: 50%;
    flex: none;
}
.header {
    background-image: repeating-linear-gradient(
        to left,
        violet,
        indigo,
        blue,
        green,
        yellow,
        orange,
        red
    );
    -webkit-background-clip: text;
    -webkit-text-fill-color: transparent;
    font-size: 10vw;
    margin: 0 0 0.25em;
}
img {
    max-width: 100%;
}