.certificate_roll{
    width:65%;
    overflow: hidden;
    position: relative;
    margin-left:17.5%;
}
.certificate_roll ul{
    overflow: hidden;
    position:relative;
}
.row1{
    margin:3% 0;
    margin-left:17.5%;
}
.row1 li{
    float:left;
    overflow: hidden;
}
.row1 li img{
    width:100%;
    float:left;
}
.bg_color{
    padding:3% 0;
    background:#f0f0f0;
}
.row2 li{
    float:left;
    overflow: hidden;
}
.row2 li img{
    width:100%;
    float:left;
}