[csswg-drafts] [css-values-4] 'lh' and 'rlh' unit need to explain how to convert to an absolute length

dbaron has just created a new issue for https://github.com/w3c/csswg-drafts:

== [css-values-4] 'lh' and 'rlh' unit need to explain how to convert to an absolute length ==
The definitions of [the `lh` unit](https://drafts.csswg.org/css-values/#lh) and the `rlh` unit need to explain how to convert a line-height to an absolute length.  In particular, this is interesting for `normal`, and it probably needs to say that it uses the first available font (which isn't the way `normal` works in layout).

(This came out of the discussion the WG is currently having.)

Please view or discuss this issue at https://github.com/w3c/csswg-drafts/issues/1253 using your GitHub account