[idea] dark/light-specific custom theme colors for auto_switch

[wiscaksono]

idea / problem

I'm building a GitHub theme for herdr. Dark mode needs accent=#2f81f7, panel_bg=#0d1117. Light mode needs accent=#0969da, panel_bg=#ffffff. But [theme.custom] uses the same hex values for both modes. So I can't get both looking right with auto_switch on.

requested change

Support dark/light-specific sections in [theme.custom]. Something like:

[theme.custom.dark]
accent = "#2f81f7"
panel_bg = "#0d1117"

[theme.custom.light]
accent = "#0969da"
panel_bg = "#ffffff"

Existing [theme.custom] keys stay as fallback for both modes. Mode-specific sections take precedence when active.

why you want this

I use Ghostty with a GitHub theme. herdr inherits terminal colors fine, but the UI chrome (accent, borders, panel bg) needs different values for dark and light. Right now I have to pick one mode or the other. With auto-switch and mode-specific custom colors, I get a proper GitHub look in both.

[aneym]

I ran into this from the other direction and landed on the same shape you proposed here.

My case was sidebar ink rather than a full theme. Row titles needed a lighter text value to read well in Mocha. Once auto-switch flipped to Latte, those values washed out against the light background and the titles became the hardest thing on screen to read. A single value that works in both modes means a value that is mediocre in both.

I have your proposal implemented and have been running it locally for several days. It follows the precedence you described: theme defaults, then [theme.custom] for both modes, then [theme.custom.light] or [theme.custom.dark] for the resolved appearance. Configs that do not use the new blocks resolve exactly as they do today.

[theme]
auto_switch = true

[theme.custom]
accent = "#fe640b"

[theme.custom.light]
text = "#2e3145"
subtext0 = "#494c66"

Both panes are the same seeded layout at the same size, rendered with catppuccin-latte active. The only difference is the [theme.custom.light] block. On the left, text and subtext0 hold values chosen for Mocha, and the workspace names fade into the panel.

The change is 7 files, +383/-8, with docs and tests covering parse and per-mode resolution. It cherry-picks onto current master with no conflicts, and just check is clean: fmt, clippy, config-reference parity, and nextest at 3034 passing with 3 failures that reproduce unchanged on master.

@ogulcancelik, is this a direction you want in config? CONTRIBUTING says features start here, so I am asking before sending anything. If you want it I can open a PR against master; if the shape should be different, say how and I will rework it. #2032 asks for the same capability from a full-theme-pair angle, so whatever shape you prefer should probably cover both.

[ogulcancelik]

yep i think we miss a theme.custom.light and theme.custom.dark when theme is custom. sounds good. you can send a pr in that context

[aneym]

Opened #2324.

[aneym]

The PR gate closed #2324 automatically — it admits non-maintainer PRs only with a fix: title. The branch is ready for review whenever you reopen it.