Themes and command palette improvements

[darrenburns]

• Removes App.dark
• Adds App.theme: Reactive[str] which can be used to set the theme (registered themes only).
• Adds variant parameter to Label (success/primary/accent/error, etc.)
• Adds InvalidThemeError, raised when an unregistered theme is set.
• Adds App.get_theme(theme: str) -> Theme
• Adds App.register_theme(theme: Theme)
• Adds App.unregister_theme(theme: Theme)
• Adds App.theme_changed_signal: Signal[Theme].
• Adds App.available_themes -> dict[str, Theme]
• Fix Select widget sometimes immediately re-opening when closed with a click of the mouse
• Allows CommandPalette to be instantiated and pushed by users, with arbitrary providers and a custom placeholder per-instance.
• Added SimpleProvider which allows a caller to pass commands into a CommandPalette rather than having a provider be aware of where it might be invoked (experiment).
• Added App.search, a shorthand for the above that lets you quickly invoke a searchable menu with a list of commands, e.g. self.app.search([("copy", self.copy), ("paste", self.paste)] (an experiment - creating a separate provider each time feels like a big overhead and the providers need to query the active screen etc.)
• Adds App.search_themes which pulls up a command palette containing all registered themes. This is what is called when you select "Change theme" in the command palette.
• Defines some new builtin CSS vars $hover, $cursor-highlight, $cursor-highlight-blurred, $hover-highlight, $hover-highlight-blurred.
• Tries to make usage of variables a bit more consistent without changing the look and feel of Textual.
• Changes tree and data table cursors to match other cursors, and removes the "green" accent from the tree lines.
• Updates a bunch of widgets to use nested CSS instead of flat CSS as it seems easier to read and keep related rules together.
• I tried to make RadioSet look a bit more like SelectionList - haven't quit achieved what I intended there though.
• All widgets with a "highlight cursor" (the blue rectangle behind the highlighted option) now have a "blurred" version of that cursor, so when the widget loses focus, the cursor fades slightly.
• Some widgets had an underline indicating the "highlighted" option (e.g. RadioSet) - I replaced this with a cursor (just changing the styles). It's more coherent/consistent with other widgets, and also gains the "blurred" cursor effect when it loses focus. I'm not sure it looks better in isolation 🤷
• Added consistent block cursor styling.

textual-themes-3oct24__89pct_smaller.mp4

Widget borders

I tried removing the widget borders and although I do think they look better in isolation, when they touch each other there's no way to distinguish between them:

I opted to keep the border but make it very subtle:

Background tint

The majority of builtin widgets now get a subtle background tint when focused e.g:

This is particularly useful for users who prefer compact styles and remove borders and therefore don't receive the "focus styling" that gets applied to borders.

[willmcgugan]

I think the quotes may confuse there. It suggests that they are strings.

Maybe something along these lines?

Themes may be marked as being light or dark.

[willmcgugan]

😢

[willmcgugan]

I kinda liked the original spelling better.

[TomJGooding]

I spotted that the unselected crosses in the SelectionList aren't visible in the textual-light theme, was this intentional? I just thought I'd check as the similar widgets look okay.

I'm also finding it a bit difficult to make out the scrollbar on the screen in light mode, but maybe that's just to my eyes! Especially in 256-color terminals where the thumb barely distinguishable . Hope you don't mind my late feedback, I realise this has already been merged...

[darrenburns]

Thanks Tom, we're doing another pass now before releasing this. Tweaking scrollbars now, but didn't notice the issue with the SelectionList - will get that sorted too. Cheers!

[TomJGooding]

Sorry I've also just spotted there's a similar issue in the RadioSet when focused (the scrollbar looks better now!)

[darrenburns]

@TomJGooding cheers - working on SelectionList, RadioSet and ToggleButton now! Will try to make them consistent on light themes.

[TomJGooding]

Sorry will leave this now in your capable hands! This is a fantastic feature and I can see the work that's gone into it, hopefully you don't think I'm just nitpicking.

[darrenburns]

No no, not at all! We appreciate it. This was so much ground to cover and I definitely missed a few things. If you find anything else that you think looks off please let us know :)