html, 
body {
    display: block;
    height: 100%;
    position: relative;
}

body {
   width:1000px;
margin:0 auto;
}

.main {
    width: 100%;
}

.overlay {
    background: rgba(0, 0, 0, .5);
    bottom: 0;
    box-sizing: border-box;
    display: none;
    height: 100%;
    left: 0;
    outline: none;
    overflow: auto;
    position: absolute;
    right: 0;
    top: 0;
    z-index: 1000;
}

.dialog { 
    background: #fff;
    color: #444;
    margin: 20px auto;
    padding: 20px;
    position: relative;
    width: 640px;
}