Misc docs fixes

[casey]

• Add description of name encoding on theory page
• Vertically align contents of nav bar and make logo bold and white
• Don't color block links on homepage by rarity (in practice, they're always an ugly green color)
• Use CSS variables for colors
• Use coal as the default theme for the book
• Style the site with coal theme colors (we can change this later, I just want both to be the same color)