css - 带有背景图像的元素上的阴影？

Question

在下面的示例中，我有两个元素。一个有内容部分的背景图像，另一个没有。两个 header 都有一个 box-shadow 属性。如何使阴影在设置了背景图像的元素上方可见？

.testcontainer {
  width: 200px;
  display: inline-block;
  border: 1px solid gray;
  height: 120px;
}

.header {
  height: 20px;
  background-color: cornflowerblue;
  color: white;
    -webkit-box-shadow: 0 2px 2px 0 rgba(0, 0, 0, 0.14), 0 3px 1px -2px rgba(0, 0, 0, 0.12), 0 1px 5px 0 rgba(0, 0, 0, 0.2);
          box-shadow: 0 2px 2px 0 rgba(0, 0, 0, 0.14), 0 3px 1px -2px rgba(0, 0, 0, 0.12), 0 1px 5px 0 rgba(0, 0, 0, 0.2);
}

.content {
  height: 100px;
}

#hasbgimage {
  background-image: url("https://via.placeholder.com/200x100");
  background-size: cover;
}

<div class="testcontainer">
  <div class="header">test with no image</div>
  <div class="content"></div>
</div>
<div class="testcontainer">
  <div class="header">test with image</div>
  <div class="content" id="hasbgimage"></div>
</div>

Answer 1

您可以简单地将 z-index 添加到第一个元素，使其 box-shadow 也位于上方

.testcontainer {
  width: 200px;
  display: inline-block;
  border: 1px solid gray;
  height: 120px;
}

.header {
  position:relative; /*And don't forget this !!!*/
  z-index:2;
  height: 20px;
  background-color: cornflowerblue;
  color: white;
    -webkit-box-shadow: 0 2px 2px 0 rgba(0, 0, 0, 0.14), 0 3px 1px -2px rgba(0, 0, 0, 0.12), 0 1px 5px 0 rgba(0, 0, 0, 0.2);
          box-shadow: 0 2px 2px 0 rgba(0, 0, 0, 0.14), 0 3px 1px -2px rgba(0, 0, 0, 0.12), 0 1px 5px 0 rgba(0, 0, 0, 0.2);
}

.content {
  height: 100px;
}

#hasbgimage {
  background-image: url("https://via.placeholder.com/200x100");
  background-size: cover;
}

<div class="testcontainer">
  <div class="header">test with no image</div>
  <div class="content"></div>
</div>
<div class="testcontainer">
  <div class="header">test with image</div>
  <div class="content" id="hasbgimage"></div>
</div>