box shadow not working

问题

I'm trying to add a box shadow to #main-content-area on the top side and 50% to both the left and right sides (from top), but it is not working.

What is wrong with my code?

.wrapper {
  position: relative;
}
#main-content-area {
  position: relative;
  background-color: white;
  margin: -80px auto auto auto;
  z-index: 4;
  border: 1px solid red;
}
.halfshadow {
  position: absolute;
  z-index: -1;
  top: 0;
  height: 50%;
  box-shadow: 1px 0px 10px rgba(0, 0, 0, 0.5);
}

<div class="wrapper">
  <div class="line"></div>
  <div class="row">
    <div class="col-sm-2">
    </div>
    <div class="col-sm-8" id="main-content-area">

      <div class="row">
        <div class="col-sm-4">
          <img src="me.jpg" class="img-responsive" />
        </div>

        <div class="col-sm-4">
          <img src="me.jpg" class="img-responsive" />
        </div>

        <div class="col-sm-4">
          <img src="me.jpg" class="img-responsive" />
        </div>
      </div>

    </div>
    <div class="halfshadow"></div>

    <div class="col-sm-2">
    </div>
  </div>
</div>

回答1:

Just for showing box-shadow I have removed the position: absolute; you can position your div as per your requirement.

.wrapper{
  position:relative;
}

#main-content-area{
  position:relative;
  background-color:white;
  margin: -80px auto auto auto;
  z-index:4;
  border:1px solid red;
}
 
.halfshadow{
  z-index:-1;
  height: 50px;
  width: 100%;
  box-shadow: 1px 0px 10px rgba(0, 0, 0, 0.5);
}

<div class="wrapper">
  <div class="line"></div>
  <div class="row" >
    <div class="col-sm-2"></div>
    <div class="col-sm-8" id="main-content-area">
      <div class="row">
        <div class="col-sm-4">
          <img src="me.jpg" class="img-responsive"/>
        </div>
        <div class="col-sm-4">
          <img src="me.jpg" class="img-responsive"/>
        </div>
        <div class="col-sm-4">
          <img src="me.jpg" class="img-responsive"/>
        </div>
      </div>
    </div>
    <div class="halfshadow"></div>
    <div class="col-sm-2" ></div>
  </div>
</div>

回答2:

use width "halfshadow" div or place content. Here is example with added "width"

.halfshadow {
position: absolute;
z-index: -1;
top: 0;
height: 50%;
width: 100%;
box-shadow: 1px 0px 10px rgba(0, 0, 0, 0.5);
}

回答3:

Remove position: absolute; from .halfshadow class

回答4:

you need to mention div tag

.div1
{
  padding: 28px 10px;
  /* width: 230px; */
  width:200px;
  /*  margin-right: 31px;
  margin-left: 105px;*/
  margin-top:10px;
  height: 226px;
  box-shadow: 10px 10px 5px #888888;
  margin-top: -20px;
  color: blue;
  text-align: center;
}

来源：https://stackoverflow.com/questions/41391849/box-shadow-not-working