1、上下居中(垂直居中)
style="height: 28px;
display: flex;
flex-direction: row;
align-items: center;"
2、左右居中(水平居中)
style="height: 28px;
display: flex;
flex-direction: row;
justify-content: center;"
3、左右居中(水平居中)
style="display: flex;
flex-direction: column;
align-items: center;"
4、居中(水平、垂直居中)
style="height: 28px;
display: flex;
flex-direction: row;
align-items: center;
justify-content: center;
background: #b2b2c5;
border-radius: 2px"
效果预览: