添加图像复盖的颜色

N

footer#site-footer{  
  position:relative;
}

footer#site-footer:before {     /* use before property (pseudo-element)  */
    position: absolute;
    content: '';
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    background: rgba(0,0,0,0.3);
}