水平垂直居中的方式（3种）

<div class="parent">
<div class="child">哈哈哈</div>
</div>

.parent{
position: relative;
background: pink;
width: 200px;
height: 200px;
margin: 0 auto;

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

.parent{
text-align: center;
display: table-cell;
vertical-align: middle;
background: pink;
width: 200px;
height: 200px;
margin: 0 auto;
}
.child{
display: inline-block;
background: red;
}

.parent{
display: flex;
justify-content: center;
align-items: center;
background: pink;
width: 200px;
height: 200px;
margin: 0 auto;
}
.child{
background: red;
}