Positioning setting horizontal and vertical center (multiple methods)

Method 1 ：flex

Set in parent box ：
display : flex;
align-items: center;
justify-content: center;

Method 2 ： float

The son is the father
left ：50%
top ：50%
transfrom: transletter(-50%,-50%)

Method 3 ：

Horizontal center （text-align）： center
Vertical center （line-height）: Same height as the current block