overflow为什么所有的图片都不见了啊，求解答
@charset"utf-8";
*{
margin:0px;
padding:0px;
font-size:12px;
}
body{
background-color:#f5f5f5;
}
.top{
width:100%;
height:27px;
background:url(../images/top_bg.jpg) repeat-x;
}
.top_content{
width:1000px;
margin:0 auto;
}
.top_content li{
list-style-image:url(../images/li_bg.gif);
float:right;
width:70px;
line-height:27px;
}
.top_content li a:link,.top_content li a:visited{
text-decoration:none;
color:#8e8e8e;
}
.top_content li a:hover,.top_content li a:active{
color:#900;
text-decoration:none;
}
.wrap{
width:1000px;
margin:0 auto;
}
.logo{
height:83px;//后来我发现把这里的高度增加三个像素就可以了，但是不知道是为什么，希望您能帮我解答下，谢谢啦
background-color:#fff;
}
.logo_left{
width:200px;
float:left;
}
.logo_right{
width:300px;
float:right;
height:28px;
margin-top:30px;
color:#8e8e8e;
}
.logo_right img{
vertical-align:middle;
margin-right:10px;
}
.tel{
font-family: "微软雅黑";
font-size: 16px;
color:#c00;
}
.nav{
height:40px;
}
.nav_left{
width:10px;
background:url(../images/nav_left.jpg) no-repeat;
height:40px;
float:left;
}
.nav_mid{
width:980px;
background:url(../images/nav_bg.jpg) repeat-x;
float:left;
}
.nav_right{
width:10px;
background: url(../images/nav_right.jpg) no-repeat;
height:40px;
float:left;
}
.nav_mid_left{
width:680px;
float:left;
}
.nav_mid_right{
width:300px;
float:right;
}
.nav_mid_left li{
float:left;
list-style-type: none;
width:90px;
text-align:center;
line-height:40px;
}
.nav_mid_left a{
display:block;
}
.nav_mid_left a:link,.nav_mid_left a:visited{
text-decoration: none;
color:#fff;
font-family: "微软雅黑";
font-size: 16px;
}
.nav_mid_left a:hover,.nav_mid_left a:active{
text-decoration: none;
background-color:#ca394a;
font-family: "微软雅黑";
font-size: 16px;
}
.search_text{
width:190px;
height:25px;
margin-top:7px;
background:url(../images/search.jpg) no-repeat right center;
background-color: #fff;
padding-right:25px;
border:1px solid #fff;
}
.ad{
height:310px;
overflow:hidden;
}
请给代码