Vertical center in CSS, different from table

Vertical center is a piece of cake for tables. You only need to specify the cell as vertical-align: Middle,
But this does not work in CSS layout. Suppose you set the height of a navigation menu to 2em,
Then, specify the vertical alignment rules in CSS, and the text will still be ranked at the top of the box. There is no difference at all.
To solve this problem, you only need to set the Row Height of the box to the same as the height of the box,
In this example, the box height is 2em, so you only need to add one more line-Height: 2em in CSS to implement vertical