Fixing the green header bar to the viewport is not a bad idea but once again badly implemented. For a start it cuts off the tops of posts if you follow a link directly to one, it also doesn't play nicely with logos and menus. Having made my living building websites in the past I can say I would not have expected to receive my full fee for everything that's been done to TSR over the last couple of months, not because it's aesthetically displeasing (although it is) but because it's shoddy work.
If you're determined to burn time and money on this, can I suggest doing something useful rather than unnecessary cosmetic changes which please nobody. You might start by considering mobile accessibility.