body {
    background-image: 
        url('../assets/images/background.png'), /* 左侧背景图 */
        url('../assets/images/background.jpg'); /* 右侧背景图 */
    background-size: auto 30%, 20% auto; /* 两个图都缩小到原始大小的50% */
    background-position: left bottom, right bottom; /* 左侧图在左下角，右侧图在右下角 */
    background-repeat: no-repeat;
    background-attachment: fixed;
}