css3如何给背景图片加颜色遮罩？

在开发中，有时遇到需要给背景层加颜色遮罩的项目，现在特定总结一下给背景图层加颜色遮罩的方法。

方法一：通过定位叠加(注意层级)

<p class="wrap1">
     <p class="inner"> </p>
</p>
.wrap1 {
    position: relative;
    width: 1200px;
    height: 400px;
    background: rgba(0, 0, 0, .5);
}

.wrap1 .inner {
    position: absolute;
    left: 0;
    right: 0;
    top: 0;
    bottom: 0;
    background: url(ban8.jpg) no-repeat center center;
    background-size: cover;
    z-index: -1;
}

方法二：通过伪类元素叠加

<p class="wrap2"></p>
.wrap2 {
    position: relative;
    width: 1200px;
    height: 400px;
    background: url(ban8.jpg) no-repeat center center;
    background-size: cover;
}

.wrap2::before {
    content: "";
    position: absolute;
    left: 0;
    right: 0;
    bottom: 0;
    top: 0;
    background-color: rgba(0, 0, 0, .5);
    z-index: 2;
}

方法三：CSS3颜色叠加background-blend-mode:multiply;(正片叠底)

<p class="wrap3"></p>
.wrap3 {
    position: relative;
    width: 1200px;
    height: 400px;
    background: url(ban8.jpg) rgba(0, 0, 0, .5) no-repeat center center;
    background-blend-mode: multiply;
}

拓展：背景模糊加颜色叠加

.wrap4 {
    position: relative;
    width: 1200px;
    height: 400px;
    background: url(ban8.jpg) rgba(0, 0, 0, .5) no-repeat center center;
    background-blend-mode: multiply;
    filter: blur(2px);
    overflow: hidden;
}