Picker separator below input line lacks a theme key

[kyrime]

Currently, the picker separator is hardcoded to the default theme's comet color (purplish). The relevant code is at https://github.com/helix-editor/helix/blob/master/helix-term/src/ui/picker.rs#L590.

[the-mikedavis]

We should be able to replace that line:

helix/helix-term/src/ui/picker.rs

Line 590 in e8e2526

let sep_style = Style::default().fg(Color::Rgb(90, 89, 119));

with something like:

let sep_style = cx.editor.theme.get("ui.text.separator");

and add the new scope to the default theme here:

helix/theme.toml

Lines 54 to 56 in e8e2526

	"ui.text" = { fg = "lavender" }
	"ui.text.focus" = { fg = "white" }
	"ui.virtual" = { fg = "comet" }

as comet.

The scope name might need some bike-shedding. Would you like to open a PR?

[kyrime]

The key name/scope is the reason I didn't open a PR, haha. Since the borders of the picker use ui.background as their key I was thinking it should be ui.background.separator to draw a reasonable default for all the other themes, but then I thought ui.background isn't the most descriptive name for borders in the first place and decided to just leave it to someone more familiar with the theme key names. I'll open a PR.

[the-mikedavis]

Hmm yeah I'm not sure what the best scope name for this would be either 😅

What do others think?