chore(config): add shared tailwind.config.css outer shell

Introduces `packages/config/tailwind.config.css` as the CSS-first
orchestration layer shared by every app. It collects three things that
were previously duplicated across every app's main CSS entry:

- `@import` of `packages/ui/build/css/source/global.css` — the design
  system's CSS variable definitions.
- `@import` of `dark.css`, `light.css`, and `classic-dark.css` — per-mode
  overrides for those variables.
- `@import` of `packages/config/tailwind-utilities/hit-area.css` — the
  v4-native `hit-area-*` utility port.

And one new thing:

- `@custom-variant dark` matching v3's
  `darkMode: ['class', '[data-theme*='dark']']` — active on `.dark` or
  `[data-theme*='dark']`, on the element itself or any ancestor, with
  zero-specificity via `:where()`.

Every app's main CSS entry now reads:

  @import 'tailwindcss';
  @import '.../packages/config/tailwind.config.css';
  @import './tailwind.config.css';
  @config '.../packages/config/tailwind.config.js';

The four duplicated imports (global + three themes + hit-area) disappear
from each app's entry file. The `@config` bridge stays for now; the
declarative theme still lives in the JS config. The next commit will
merge `tailwind.config.js` and `ui.config.js` into a single JS plugin
loaded by this CSS file, at which point the `@config` line goes away.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

apps/design-system/styles/globals.css

@@ -1,11 +1,7 @@
 @import 'tailwindcss';
+@import './../../../packages/config/tailwind.config.css';
 @import './tailwind.config.css';
 
-@import './../../../packages/ui/build/css/source/global.css';
-@import './../../../packages/ui/build/css/themes/dark.css';
-@import './../../../packages/ui/build/css/themes/classic-dark.css';
-@import './../../../packages/ui/build/css/themes/light.css';
-
 @config '../../../packages/config/tailwind.config.js';
 
 @import 'config/typography.css';

apps/docs/styles/main.css

@@ -1,10 +1,6 @@
 @import 'tailwindcss';
+@import './../../../packages/config/tailwind.config.css';
 @import './tailwind.config.css';
-@import './../../../packages/config/tailwind-utilities/hit-area.css';
-
-@import './../../../packages/ui/build/css/source/global.css';
-@import './../../../packages/ui/build/css/themes/dark.css';
-@import './../../../packages/ui/build/css/themes/light.css';
 
 @config '../../../packages/config/tailwind.config.js';
 

apps/learn/styles/globals.css

@@ -1,11 +1,7 @@
 @import 'tailwindcss';
+@import './../../../packages/config/tailwind.config.css';
 @import './tailwind.config.css';
 
-@import './../../../packages/ui/build/css/source/global.css';
-@import './../../../packages/ui/build/css/themes/dark.css';
-@import './../../../packages/ui/build/css/themes/classic-dark.css';
-@import './../../../packages/ui/build/css/themes/light.css';
-
 @config '../../../packages/config/tailwind.config.js';
 
 @layer base {

apps/lite-studio/app/app.css

@@ -1,10 +1,6 @@
 @import 'tailwindcss';
+@import './../../../packages/config/tailwind.config.css';
 @import './tailwind.config.css';
-@import './../../../packages/config/tailwind-utilities/hit-area.css';
-
-@import './../../../packages/ui/build/css/source/global.css';
-@import './../../../packages/ui/build/css/themes/dark.css';
-@import './../../../packages/ui/build/css/themes/light.css';
 
 @config '../../../packages/config/tailwind.config.js';
 

apps/studio/styles/main.css

@@ -1,11 +1,6 @@
 @import 'tailwindcss';
+@import './../../../packages/config/tailwind.config.css';
 @import './tailwind.config.css';
-@import './../../../packages/config/tailwind-utilities/hit-area.css';
-
-@import './../../../packages/ui/build/css/source/global.css';
-@import './../../../packages/ui/build/css/themes/dark.css';
-@import './../../../packages/ui/build/css/themes/light.css';
-@import './../../../packages/ui/build/css/themes/classic-dark.css';
 
 @import 'config/typography.css';
 

apps/ui-library/styles/globals.css

@@ -1,11 +1,6 @@
 @import 'tailwindcss';
+@import './../../../packages/config/tailwind.config.css';
 @import './tailwind.config.css';
-@import './../../../packages/config/tailwind-utilities/hit-area.css';
-
-@import './../../../packages/ui/build/css/source/global.css';
-@import './../../../packages/ui/build/css/themes/dark.css';
-@import './../../../packages/ui/build/css/themes/classic-dark.css';
-@import './../../../packages/ui/build/css/themes/light.css';
 
 @config '../../../packages/config/tailwind.config.js';
 

apps/www/styles/index.css

@@ -1,10 +1,6 @@
 @import 'tailwindcss';
+@import './../../../packages/config/tailwind.config.css';
 @import './tailwind.config.css';
-@import './../../../packages/config/tailwind-utilities/hit-area.css';
-
-@import './../../../packages/ui/build/css/source/global.css';
-@import './../../../packages/ui/build/css/themes/dark.css';
-@import './../../../packages/ui/build/css/themes/light.css';
 
 @config '../../../packages/config/tailwind.config.js';
 

packages/config/tailwind.config.css

@@ -0,0 +1,26 @@
+/*
+ * Shared Tailwind v4 config for all Supabase apps.
+ *
+ * This file is the CSS-first orchestration layer. The imperative theme
+ * configuration (colors, typography, keyframes, custom plugins, etc.) still
+ * lives in the sibling `tailwind.config.js` and is loaded via the `@config`
+ * directive from each app's main CSS entry. That will migrate here in a
+ * follow-up commit.
+ */
+
+/* Core CSS variable definitions for the Supabase design system. Defines
+ * --foreground-*, --background-*, --border-*, etc. */
+@import '../ui/build/css/source/global.css';
+
+/* Per-mode overrides for the CSS variables above. */
+@import '../ui/build/css/themes/dark.css';
+@import '../ui/build/css/themes/light.css';
+@import '../ui/build/css/themes/classic-dark.css';
+
+/* v4-native port of the custom `hit-area-*` utilities (from bazza.dev). */
+@import './tailwind-utilities/hit-area.css';
+
+/* Dark mode: matches v3's `darkMode: ['class', '[data-theme*="dark"]']` —
+ * activates on `.dark` or `[data-theme*='dark']`, on the element itself
+ * or any ancestor. `:where()` keeps specificity at 0. */
+@custom-variant dark (&:where(.dark, .dark *, [data-theme*='dark'], [data-theme*='dark'] *));