Is it possible to make a div 50px less than 100% in CSS3? [duplicate]

Answer 1

jsFiddle

Using display block and margin. display:block when not combined with a defined height/width will try to fill it's parent.

header {
    width:100%;
    background:#d0d0d0;
    height:100%;
}
h1 {
    display:block;
    border:#000 solid 1px;
    margin:0 50px 0 0;
    height:100px;
}