z-index only works on positioned elements (position:absolute, position:relative, or position:fixed).
So, try like:
.app1 {
background: url("../images/Backgound.png") repeat-y scroll left top transparent;
height: 1000px;
width: 400px;
margin-left: 500px;
position:relative;
z-index: 999999 !important;
}