div 居中

方法1 margin

.box{
	width: 100px;
	height: 100px;
	background-color: red;
	position: absolute;
	left: 50%;
	top: 50%;
	margin-left: -50px;
	margin-top: -50px;
}			

方法2 CSS3 transform-translate

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

方法3 flex

.box {
	display: flex;
	background-color: red;
	height: 400px;
	width: 400px;
	align-items: center;
	justify-content: center;
}

.box2 {
	height: 100px;
	width: 100px;
	background-color: pink;
}

<div class="box">
	<div class="box2">
	</div>
</div>

方法4 转换为inline

.box {
	background-color: red;
	height: 400px;
	width: 400px;
	text-align: center;
	line-height: 400px;
}

.box2 {
	display: inline;
	background-color: pink;
}
<div class="box">
    <div class="box2">
        内容内容
    </div>
</div>