应用旋转可打破阴影效果

Question

我正在尝试将旋转应用于div。

但是，当我这样做时，它破坏了上面的“纸影效果”。为什么？

该如何保持这种效果？

.test {
  position: relative;
  margin: 20px auto;
  width: 300px;
  height: 100px;
  border: 1px solid #ccc;
  background: #fff;
}

.test:before {
  z-index: -1;
  position: absolute;
  content: "";
  bottom: 15px;
  left: 12px;
  width: 45%;
  height: 20px;
  background: #777;
  -webkit-box-shadow: 0 15px 19px #aaa;
  -moz-box-shadow: 0 15px 19px #aaa;
  box-shadow: 0 15px 19px #aaa;
  -webkit-transform: rotate(-3deg);
  -moz-transform: rotate(-3deg);
  -o-transform: rotate(-3deg);
  -ms-transform: rotate(-3deg);
  transform: rotate(-3deg);
}

.test:after {
  z-index: -1;
  position: absolute;
  content: "";
  bottom: 15px;
  right: 12px;
  width: 45%;
  height: 20px;
  background: #777;
  -webkit-box-shadow: 0 15px 19px #aaa;
  -moz-box-shadow: 0 15px 19px #aaa;
  box-shadow: 0 15px 19px #aaa;
  -webkit-transform: rotate(3deg);
  -moz-transform: rotate(3deg);
  -o-transform: rotate(3deg);
  -ms-transform: rotate(3deg);
  transform: rotate(3deg);
}

<div class="test">Without transform</div>

<div class="test" style="transform:rotate(2deg)">With transform:rotate(2deg)</div>

Answer 1

这是因为transform create a stacking context将阴影放置在容器内部而不是外部。例如，如果您向容器中添加z-index值，则会遇到相同的问题：

要解决此问题，您可以考虑采用另一种方法，如下所示：

.test {
  position: relative;
  margin: 20px auto;
  width: 300px;
  height: 100px;
  border: 1px solid #ccc;
  z-index: 0;
}


/*this will create the shadow*/

.test:before {
  z-index: -2;
  position: absolute;
  content: "";
  bottom: 0;
  left: 15px;
  right: 15px;
  height: 10px;
  background:
   linear-gradient(to top right, transparent 49.5%, #aaa 50%) top right/50% 100%, 
   linear-gradient(to top left, transparent 49.5%, #aaa 50%) top left/50% 100%;
  background-repeat: no-repeat;
  filter: drop-shadow(0 7px 5px #aaa);
}


/*this will be your background*/

.test:after {
  z-index: -1;
  position: absolute;
  content: "";
  top: 0;
  bottom: 0;
  right: 0;
  left: 0;
  background: #fff;
}

<div class="test">Without transform</div>

<div class="test" style="transform:rotate(2deg)">With transform:rotate(2deg)</div>