.ad {

display: block;
position: fixed;
width: 984px;
height: 170px;
margin-right: auto;
margin-left: auto;
left: 0;
right: 0;
top: -40px;
-webkit-transition: top 2s; /* Safari */
transition: top 2s;
z-index: 100;
background-color: #fff;

}

.ad img {
	width: 984px;
	height: 170px;
	cursor: pointer;

}