html {
    display: flex;
    justify-content: center;
    align-items: center;
    width: 100%;
    height: 100%;
    background: url(bitmerang.png) center center no-repeat #e94f35;
    background-size: 80%;
}

@media (min-width: 800px) {
    html {
        background-size: auto;
    }
}