Updated background

Slight update to 'Lost'.  I changed the background to a gradient colour scheme, using the four colours you can choose from in the game.  Took a bit of doing, but I got there with help from the folks on the Twine subreddit.

I've kept the background behind the text black, so that it's still readable.  It's a bit close around the borders/margins, but it shouldn't be a problem.  Someone let me know if it is, and I'll try to fix it.  Not sure how, but I'm sure the subreddit would know.