How to make a child div transparent?

Question

Suppose there is a div, say \"parent-div\". The parent div has a background color. What if the child div, \"child-div\", needs to be set with a transparen

Answer 1

Don't apply background on .parent-div.

Instead use a large value of box-shadow on .child-div and add overflow: hidden on .parent-div to hide unwanted shadow effect.

Following css will do the work:

.parent-div {
  overflow: hidden;
}
.child-div {
  box-shadow: 0 0 0 500px #f00;
}

.wrapper {
  background-image: url('http://media.istockphoto.com/photos/medium-golden-brown-wood-texture-background-picture-id513694258?k=6&m=513694258&s=170667a&w=0&h=xETakP7VjpAtRj9e6rJRYNqw_AJLZ9ovLlC4ebR5BOQ=');
}

.parent-div {
  overflow: hidden;
  width: 100px;
  height: 100px;
  padding: 10px;
  margin: auto;
}

.child-div {
  box-shadow: 0 0 0 500px #f00;
  border: 1px solid;
  width: 60%;
  height: 60%;
  margin: auto;
  
}

<div class="wrapper">
  <div class="parent-div">
    <div class="child-div">
    </div>
  </div>
</div>

Answer 2

Check this Fiddle

based on:

.parent{
    width:300px;
    height:300px;
    position:relative;
    border:1px solid red;
}
.parent:after{
    content:'';
    background:url('http://www.dummyimage.com/300x300/000/fff&text=parent+image');
    width:300px;
    height:300px;
    position:absolute;
    top:0;
    left:0;
    opacity:0.5;
}
.child{
    background:yellow;
    position:relative;
    z-index:1;
}

ref