`idiomatic css` for the clock app only or entirely in Gaia, because I don't know anything about Gaia? Hope that you know this one https://wiki.mozilla.org/Gaia/CSS_Guidelines ... we are trying to follow this simple guideline (I know it's not perfect) but if each app have its own CSS guide ... this will make me very sad I need to remember a lot of things :D 

anyway ... for this case I will update the code :)