#modal_wrapper.overlay::before {
content: " ";
width: 100%;
height: 100%;
position: fixed;
z-index: 100;
top: 0;
left: 0;
background: #000;
background: rgba(0,0,0,0.7);
}
#modal_window {
display: none;
z-index: 200;
position: fixed;
left: 50%;
top: 50%;
width: 970px;
height: 480px;
overflow: auto;
padding: 10px 20px;
background: #fff;
border: 5px solid #999;
border-radius: 10px;
box-shadow: 0 0 10px rgba(0,0,0,0.5);
overflow-y:hidden; 
}
#modal_wrapper.overlay #modal_window {
display: block;
}