Centering an Element Relative to Another Element

Question

I have an element that should be horizontally centered to another element. The CSS for the centered element is so (I removed uneccesary code):

#center-element{
    display: flex;
    flex-direction: column;
    align-items: stretch;
    position: absolute;
}

I have to do so using vanilla JS. I tried:

var targetPos = target.getBoundingClientRect();
centerDiv.style.top = (targetPos.top + targetPos.height) + "px";
centerDiv.style.left = (targetPos.left + (targetPos.width  / 2)) + "px";

But that is off. Any ideas?

JSFiddle

Answer 1

//Somehow center the div here
var target = document.getElementById("target");
var centerDiv = document.getElementById("centerDiv");
var targetPos = target.getBoundingClientRect();
centerDiv.style.top = targetPos.bottom + "px";
centerDiv.style.left = targetPos.left + (target.offsetWidth - centerDiv.offsetWidth) / 2 + "px";

#target {
  background-color: lightblue;
  text-align: center;
  width: 75%;
}
#centerDiv {
  display: flex;
  flex-direction: column;
  align-items: stretch;
  position: absolute;
}

<div id="target">
  This is the div
</div>
<div id="centerDiv">
  This is supposed to be horizontally centered <em>to the div element above</em>
</div>

Answer 2

You can do it using flexbox. You can wrap both div inside a container div and apply display:flex; on that container.

#target {
  background-color: lightblue;
  text-align: center;
  width: 100%;
}
#centerDiv {
  /* display: flex;
  flex-direction: column;
  align-items: stretch;
  position: absolute; */
  text-align:center;
}
.container{
  display:flex;
  width:75%;
  flex-direction:column;
  align-items:center;
  justify-content:center;
}

<div class="container"><div id="target">
  This is the div
</div>
<div id="centerDiv">
  This is supposed to be horizontally centered <em><br/>to the div element above</em>
</div>
</div>