<div style="height:100px;width:100px;border:1px solid black"></div>
How can I position this div in the center?
<div style="height:100px;width:100px;border:1px solid black"></div>
How can I position this div in the center?
 
    
    .parent {
  position: relative;
}
.child {
  width: 300px;
  height: 100px;
  padding: 20px;
  position: absolute;
  top: 50%;
  left: 50%;
  margin: -70px 0 0 -170px;
}
More you find here.
 
    
    On the parent of that div:
div.parent {
  display: flex;
  justify-content: center;
  align-items: center;
}
 
    
    You can absolutely position the element with top: 50%; left: 50%; then use translate() to move it back/up 50% of it's own width to put it in the absolute center.
div {
  position: absolute;
  top: 50%; left: 50%;
  transform: translate(-50%,-50%);
}<div style="height:100px;width:100px;border:1px solid black"></div>