1、定位+外边距
.father{
position:relative;
top:50%;
left:50%;
width:40px;
height:40px;
.son{
posithon:absolute;
margin:-10px 0 0 -10px;
width:20px;
height:20px;
}
}
2、定位+位移(transform:translate(-50%,-50%))
.father{
position:relative;
top:50%;
left:50%;
width:40px;
height:40px;
.son{
posithon:absolute;
transform:translate(-50%,-50%);
width:20px;
height:20px;
}
}
3、弹性布局flex
.son{
display:flex;
justify-content:center;
align-item:center;
}