Hotfix 225

Fixes #225

@david-yz-liu As assisted by Ian (and the comments from his original pull request):

I have created a fix for the Clay issue, #225. Let me know what you think.

Also, if you think we should just stick to the old version of Clay, I will not be disappointed.

Note that (em 0) can be replaced with nil. I chose (em 0) because I think that it is easier to read, and easier to modify. All size modifications occur in lines whose sizes are either specified in em, or not at all.