html {
    background: url(colback.jpg) no-repeat center center fixed;
    -webkit-background-size: cover;
    -moz-background-size: cover;
    -o-background-size: cover;
    background-size: cover;
    text-align: center;
}
button {
    width: 150px;
    height: 50px;
    border:hidden;
}