*{
    margin: 0;
    padding: 0;
}

img{width: 300px}

.demo{
    width: 930px;
    margin-top: 20px;
    margin-left:auto ;
    margin-right: auto;
}

li{
    width: 300px;
    height: 220px;
    list-style: none;
    padding: 0;
    float: left;
    margin: 0 5px;
    position: relative;
    overflow: hidden;
}

.demo  li a{
    position: absolute;
    left: 0;
    display: block;
    width: 280px;
    height: 200px;
    top: 180px;
    background:#000;
    color: white;
    font-size: 14px;
    line-height: 25px;
    text-align: center;
    padding: 10px;
    opacity: 0.8;
    text-decoration: none;
}