Styles/themes refactoring

A complex approach to styles refactoring includes:

- [x] Separating styles and style util functions to decrease the file size and improve readability #2585
- [ ] Refactor font definitions: add missing formats of currently available font files and add fallback to available system fonts (see #2592)
- [ ] Refactor media queries to match with Bootstrap media query logic, have progressive override based on "from mobile to all unless specified otherwise" approach as demonstrated in a call (min-width: 1px ) and up
- [ ] Refactor style to not contain any "magic numbers"
- [x] Move all the theme attribute defaults from styles.clj to config-defaults.edn (#2655)
- That is, instead of `(get-theme-attribute :link-color "#025b96")` in styles.clj, add `:link-color "#025b96` to `:theme` in config-defaults.edn
- Could also document some of the theme attributes a bit at the same time
- [ ] Remove unused styles & theme variables (see TODOs in #2655)
- [ ] Refactor default theme to make sure we do not duplicate style definitions in both stylesheet and theme
```get-theme-attribute``` - remove literals and put to config defaults

Start by reading styles.clj and config-defaults.edn, then review the unchecked checklist items and the TODOs referenced from #2655, along with related issues #2592 and #2655. Done means completing and verifying the remaining font, media-query, magic-number, unused-style, and default-theme refactoring items without leaving the listed duplication or missing fallbacks.

Written by the indexing model from the issue text.