css3如何给背景图片加颜色遮罩

  第一种：
    width: 140px;
    height: 140px;
    background-blend-mode: multiply;
    filter: blur(2px);
    overflow: hidden;

 第二种：
    position: relative;
    width: 140px;
    height: 140px;
    background: url(bg.jpg) rgba(0, 0, 0, .5) no-repeat center center;
    background-blend-mode: multiply;

　　

第三种：
<div class="box">
     <div class="inner"> </div>
</div>
.box{
    position: relative;
    width: 1200px;
    height: 400px;
    background: rgba(0, 0, 0, .5);
}

.box .inner {
    position: absolute;
    left: 0;
    right: 0;
    top: 0;
    bottom: 0;
    background: url(bg.jpg) no-repeat center center;
    background-size: cover;
    z-index: -1;
}