CSS Font Sizing - Using “/”

Question

I\'ve seen sites with font-size:12px/2em (or similar) specified on the body.

What does this font sizing do exactly?

Answer 1

It's a shorthand for setting the font-size (12px) and the line-height (2em). Though, I didn't think you could do it on the font-size property, only on the font property.

Answer 2

12px is the font size and 2em is the line-height.