探索多种方法实现元素在未知或已知宽度下的精准垂直与水平居中布局

/** 1 **/
.wraper {
position: relative;
.box {
position: absolute;
top: 50%;
left: 50%;
width: 100px;
height: 100px;
margin: -50px 0 0 -50px;
}
}
/** 2 **/
.wraper {
position: relative;
.box {
position: absolute;
top: 50%;
left: 50%;
transform: translate(-50%, -50%);
}
}
/** 3 **/
.wraper {
.box {
display: flex;
justify-content:center;
align-items: center;
height: 100px;
}
}
/** 4 **/
.wraper {
display: table;
.box {
display: table-cell;
vertical-align: middle;
}
}