Forces the Fusion theme when running night mode, so we don't need
to work around platform themes that don't respond to the defined
palette.
Feedback/suggestions on the chosen colours welcome - _vars.scss is the
file to change if you want to experiment with adjustments.
- No need for the checkbox, as an unchecked box is equal to an empty
`QLineEdit`.
- The value was saved to the profile but not loaded.
- And the real pièce de résistance: I've figured out how to "Promote"
the `QLineEdit` to a `TagEdit`.
Hope you like it! :)
