code_styleguide: Filled out Javascript and some CSS

Looking back on my past pull requests, I found that a lot of comments were about my code style. (Shoutout to y'all for keeping a rigid codebase!) So, I went through my old PRs and transcribed your comments into the empty style guide. Maybe now we'll have less line comments that say "Semicolon" :+1: 

Fixes #85.

Oh yeah, it would be cool if we had conventions for CSS classes and ids, and the use of dashes vs underscores. Not sure if one was made, but it was asked before. Also, is there a convention for javascript camelCase vs snake_case?