CSS 중앙 정렬

1. transform을 이용한 중앙 정렬

<div class="parent">
	<div class="child">Centered content</div>
</div>

.parent {
  border: 1px solid #9C27B0;
  height: 250px;
  position: relative;
  width: 250px;
}

.child {
  left: 50%;
  position: absolute;
  top: 50%;
  transform: translate(-50%, -50%);
  text-align: center;
}

2. contents 중앙 정렬

<div class="container">
	<div class="center"><span>Centered content</span></div>
</div>

.container {
  border: 1px solid #9C27B0;
  height: 250px;
  width: 250px;
}

.center {
  display: table;
  height: 100%;
  width: 100%;
}

.center > span {
  display: table-cell;
  text-align: center;
  vertical-align: middle;
}

3. flex를 이용한 contents 중앙 정렬

<div class="flexbox-centering">
	<div>Centered content.</div>
</div>

.flexbox-centering {
  display: flex;
  justify-content: center;
  align-items: center;
  height: 100px;
}