Fix avatar crop screen in dark mode

What does this MR do?

Fix Avatar selector on dark mode

Before	After

Use SCSS import instead of rails require

Remove now unneeded require_self, since there's no other imports.

This slightly changes the output order (cropper CSS is no longer at the end of the file), but doesn't affect anything as the cropper styles are fairly independent.

Screenshots

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides