Custom themes

[grantm]

The app currently supports two themes - a light mode and a dark mode. Each theme is simply a collection of colour values stored in CSS custom properties (AKA "variables"). The current sets of colours are just what Grant settled on - his design skills are limited at best.

We could provide a "Theme designer" mode that allowed a user to easily assemble (and test) a set of colour values for a theme. They could use it to build multiple named themes and store them in the browser's local storage.

Users could also contribute a theme to be shared with others. The themes could simply be stored on the server as a set of JSON files (or indeed one big JSON file). The settings modal would need to allow selection of custom themes (perhaps simply through a link to the theme designer).

Theme designer features:

• Select a theme to work with (which might make it the default in the app)
• Copy an existing theme to use as a base
• Name/rename a theme
• Select a named colour value to change, provide a colour picker, and apply the users' selection (in real time?) in a preview panel
• Export to text/import from text to allow alternative editing methods
• Preview panel should have selectable (tabbed?) modes to allow user to easily test:
  • Grid view with selection and cell highlighting but no cell background colours
  • Grid view with selection, cell highlighting and no cell background colours
  • Modal view(s) (elements from hints, saved puzzles, settings ... ?)