Did a massive cleanup and refactor of shared.css, to make it more organised...

Did a massive cleanup and refactor of shared.css, to make it more organised and readable, and more consistent with naming. This included adding dashes to a few class names, and ensuring that the spelling used for words like "centre" was proper English, not US English. More modifier classes have also been prefixed with a dash, similar to how command line arguments are formatted.

Updated files that used some of these renamed CSS classes to use the new class names.