Cosmetic changes to code snippets on the site

I made some changes to the CSS code I use for code snippets on the site. Instead of the darker look with the blue dotted line I opted for the appearance of a simple text editor. I also added an effect that (in most browsers) should produce a soft highlight effect on mouse over. I think the new look is much cleaner and if I ever decided to change color schemes or templates the use of neutral colors should make the transition much easier. I also fixed a word wrap bug that would (in some cases) cause the snippet text to overflow outside the block container. I hope the new look is more intuitive.