Split out styling code instead of looping through elements

[astral-sa]

This is a prerequisite for #72.

A lot of the javascript logic, preference checking, and expensive individual element style setting that executes every page load (for every post) can be converted to some CSS

This will save us from doing so many reflows, which will speed up page re-rendering when we're applying our styles. It'll also save us some expensive running through the DOM just to craft the styles, which should speed up script execution.