[scss] Use each loop for roots.
[scss] Use each loop for sets.
[scss] Separate model sets.
[scss] Separate nav links.
[scss] Refactor nav links.
[scss] Separate JSON console theming.
[scss] Remove legend theming.
[scss] Remove @border mixin.
[scss] Move playlist styling to model-styles-sets.
[scss] Move constant margin override.
[scss] Move rest of styling out of screen.scss.

This more or less concludes the SCSS refactoring.