h1 {
    font-size: 64px;
    color: black;
    -webkit-text-stroke: 2px white;
    text-align: center;
}

h2 {
    font-size: 36px;
    color: black;
    -webkit-text-stroke: 1px white;
    text-align: center;
}

html {
    min-height: 100%;
    background:
        linear-gradient(
            rgba(255,0,0,1) 0%,
            rgba(255,154,0,1) 10%,
            rgba(208,222,33,1) 20%,
            rgba(79,220,74,1) 30%,
            rgba(63,218,216,1) 40%,
            rgba(47,201,226,1) 50%,
            rgba(28,127,238,1) 60%,
            rgba(95,21,242,1) 70%,
            rgba(186,12,248,1) 80%,
            rgba(251,7,217,1) 90%,
            rgba(255,0,0,1) 100%
        ) 0 0 / 100% 200%;
    animation: a 5s linear infinite;
}

@keyframes a {
    to {
        background-position: 0 -200%;
    }
}