Fantastic work, very cute - but you'd better get on renaming the project ASAP to avoid a cease + desist.
Nintendo does not take kindly to even the most casual use of their trademarks, even in FOSS projects.
Nintendo does not take kindly to even the most casual use of their trademarks, even in FOSS projects.
So a CSS-framework named NES should be OK.
They don't have to be right to send the letter.
There is also copyright in the design and layout of the NES interface, which has obviously been copied (it's the whole point of the project!), there's likely another option there.