Answers for "trick to center a div horizontally without flex"

how to center an item without flex

.container{
position: relative;
}
.child{
position: absolute;
top: 50%;
left: 50%;
transform: translate(-50%, 50%);
}

how to horizontally center header at the top of page with flexbox css

.box.flex {
  display: flex;
  justify-content: center;
}