bda51acb_ur___The_Web_Standards_Project__Effect
[Declaration] line-height: 1em [Effect] 
Makes the inline box of the element 12px high. This also becomes the height of the row as the only other inline box on the line is fully enclosed by this inline box. Section 10.8 of CSS 2.1 describes this in detail.
Acid2: The Guided Tour - The Web Standards Project
Effect