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I am also interested on opinions on if there is any particular coding style that would impress potential employers. I am using an internal stylesheet which I can make into a separate stylesheet if necessary. Will most employers be sophisticated enough to find my CSS no matter where I put it.
As for coding styles, usually I've found that keeping it as clean as possible is a plus (that way employers can see how you've structured your code better). Keeping your CSS in a seperate stylesheet is a bit of a nonissue recently for a single page demo, but you might as well, as that's the way you'll be coding in a job. If they can't find it then to be honest they're not the sort of people you're looking to employ you (imho).
I'd also recommend researching the sort of sites an employer makes before you get there - my previous company specialised in financial information so a candidate that came into an interview already knowledgable about how to make data tables accessible (etc) tended to be looked on more favourably than a candidate who didn't.