.linear {
        width: 630px;
        height: 120px;
        line-height: 150px;
        text-align: center;
        font-size: 26px;
        position: absolute;
        bottom: 0;
        color: #fff;
        background: -webkit-linear-gradient( top, rgba(0, 0, 0, 0),rgba(0, 0, 0, 0.2) ); /* Safari 5.1 - 6 */
        background: -o-linear-gradient(bottom,rgba(0, 0, 0, 0),rgba(0, 0, 0, 0.2)); /* Opera 11.1 - 12*/
        background: -moz-linear-gradient( bottom, rgba(0, 0, 0, 0), rgba(0, 0, 0, 0.2)); /* Firefox 3.6 - 15*/
        background: linear-gradient(to bottom,rgba(0, 0, 0, 0), rgba(0, 0, 0, 0.2)); /* 标准的语法 */
      }