Simple code to position your background to true bottom of page (without it browser place your background to bottom of screen)

bg-to-full-height.css

html {
    min-height: 100%;
    height: auto;
}
body{
    background: url("../img/bg-top.png"), url("../img/bg-middle.png"), url("../img/bg-bottom.png");
    background-repeat: no-repeat,no-repeat, no-repeat;
    background-position: top center, center center, bottom center;
}