body{
    margin: 5% auto;
    width: 80%;
    background-color: gold;
}
.content {
    position: relative;
    z-index: 2;
    padding: 30px;
    width: 100%;
    background-color: antiquewhite;
    border: solid black 2px;
}
.background {
    position: fixed;
    top: 0;
    left: 0;
    width: 100%;
    height: 50%;
    background-color: blue;
    z-index: 1;
}