Edit in JSFiddle

body {
    padding: 0;
    margin: 0;
}

html {
    height: 350px;
    font-size: 6em;
    margin: 0;
    padding: 0;
    background: -webkit-linear-gradient(#AEE8FB, #E0EFF1, #FFF);
    background: -moz-linear-gradient(#AEE8FB, #E0EFF1, #E0EFF1);
    background: -o-linear-gradient(#AEE8FB, #E0EFF1, #E0EFF1);
    background: -ms-linear-gradient(#AEE8FB, #E0EFF1, #E0EFF1);
    background: linear-gradient(#AEE8FB, #E0EFF1, #E0EFF1);
}