Move typescript quickstart CSS into separate file, rather than having it inline in the tutorial

[bfops]

[7:33 PM]phoebe: How would you feel about, instead of putting the whole stylesheet inline, slapping it in a separate document, and saying something like, "Also, go grab our stylesheet and paste it in so your app looks cool"
[7:33 PM]phoebe: Very low priority imo, but something to consider
[7:34 PM]phoebe: I suggest this only because (afaik) the stylesheet is not necessary to make the app function
[7:36 PM]3Blave: If I get the relative image stuff working, I could do the same thing for that and just have it hosted as a file. That way it'll still be in the docs repo (which is the main thing I care about)