How to position child div to the center of every parents div using position absolute in css [duplicate]

问题

This question already has an answer here:

• How to center absolutely positioned element in div? 33 answers

I'm having difficulty on positioning child div's on every parents div.

Here's the css code:

.mainDiv {
   height:500px;
   position: relative;
}

.mainDiv .parent1 {
  height: 250px;
  background-color: blue;
  top: 50px;
  position: relative;
}

.mainDiv .parent2 {
  height: 250px;
  background-color: yellow;
  position: relative;
}


.mainDiv .parent1 .sub1 {
  width: 100px;
  height: 100px;
  background-color: green;
  position: absolute;
  left: 0;
  right: 0;
  margin-left: auto;
  margin-right: auto;
  top: 50%;
}

.mainDiv .parent2 .sub2 {
  width: 100px;
  height: 100px;
  background-color: red;
  position: absolute;
  left: 0;
  right: 0;
  margin-left: auto;
  margin-right: auto;
  top: 50%;
}

Here's the fiddle

回答1:

Use transform for that to the child div and it will work!

position: absolute;
top: 50%;
left: 50%;
transform: translate(-50%, -50%);

snippet below:

.mainDiv {
  height:500px;
  
  position: relative;
}

.mainDiv .parent1 {
  height: 250px;
  background-color: blue;
   position: relative;
}

.mainDiv .parent2 {
  height: 250px;
  background-color: yellow;
   position: relative;
}


.mainDiv .parent1 .sub1 {
  width: 100px;
  height: 100px;
  background-color: green;

  position: absolute;
    left: 50%;
    top: 50%;
    transform: translate(-50%, -50%);
    
}

.mainDiv .parent2 .sub2 {
  width: 100px;
  height: 100px;
  background-color: red;
  position: absolute;
    left: 50%;
    top: 50%;
    transform: translate(-50%, -50%);
}

<div class="mainDiv">
  <div class="parent1">
    <div class="sub1">
        
    </div>
  </div>
  <div class="parent2">
    <div class="sub2">
      
    </div>
  </div>
</div>

来源：https://stackoverflow.com/questions/38892797/how-to-position-child-div-to-the-center-of-every-parents-div-using-position-abso