Add flowtheme_2026: a responsive theme with light/dark/system appearance

[martinbogo]

What this is

A modern theme for Gallery 2.3, built entirely against the existing theme API — requiredCoreApi 7.20 / requiredThemeApi 2.4, the same as matrix. No core changes are required, and it lives alongside the bundled themes without touching them.

It has been running a real ~4,300-item gallery on PHP 8.2 / Debian 12 for the work that produced #180, #181 and #183.

Design notes

• Three-state appearance. Follows the system by default; an explicit light/dark choice is remembered in localStorage. All colours are custom properties on :root, redefined once under @media (prefers-color-scheme: dark) and once under [data-theme="dark"], so the two appearances can't drift apart. color-scheme is declared so form controls and scrollbars follow too.
• Justified photo grid. Row heights come from each photo's real aspect ratio ($child.width/height) rather than the square thumbnail crop, so portraits stop being letterboxed into squares.
• Lightbox and infinite scroll are progressive enhancements. With JavaScript disabled, per-photo pages and the normal pager work unchanged — flow.js returns early if the grid isn't present, and every enhanced element degrades to a plain link.
• Styles Gallery2's own markup rather than erasing it. gcBackground1/gcBorder1, gbAdminLink lists, gbDataTable, fieldsets and submit buttons all get theme-consistent styling, so Site Admin and module views render as part of the theme instead of unstyled. (An early revision neutralised gcBackground1 to transparent; with 385 uses across 192 module templates that flattened the entire admin UI, which is worth knowing if anyone attempts something similar.)
• Ships MANIFEST and po/ scaffolding. Every user-visible string goes through i18n() / {g->text}.

Screenshot

images/screenshot.png is a synthetic placeholder, not a real capture — 505×170 to match the bundled themes, rendered programmatically from the theme's own palette tokens and showing the light and dark appearances side by side. The install it runs on is a private family gallery, so a genuine screenshot would have meant publishing personal photographs. Happy to replace it with a real capture from a demo gallery if you'd prefer, or drop the file entirely.

Testing

Exercised on a live 2.3.2 install: album grids, single-photo pages, video items, Site Admin (Plugins, Themes, Maintenance), the module views, error pages, and both appearances. Install/uninstall and switching to and from matrix both work through the normal Themes UI.

Caveats, stated plainly

• po/ contains only strings.raw and the GNUmakefile; there are no translations yet.
• The theme is new, so its API usage has been exercised against 2.3.2 but not against every module in the wild.
• I'm not assuming you want another bundled theme — if this is better off as an out-of-tree contribution, just say so and I'll close this without any hard feelings.

🤖 Generated with Claude Code

https://claude.ai/code/session_015pPeWCa9ToJFseWqbPrDH4

[martinbogo]

Apologies for not having a pretty thumbnail… I didn’t want to expose my own private photos, and I don’t have the example photo data to match the original thumbnail. “IOU” a nice thumbnail ..