Cursor rules file for Tailwind CSS v4.0

tailwind-css-v4.mdc

# Tailwind CSS v4.0

## Core Changes

- **CSS-first configuration**: Configuration is now done in CSS instead of JavaScript
  - Use `@theme` directive in CSS instead of `tailwind.config.js`
  - Example:
    ```css
    @import "tailwindcss";

    @theme {
      --font-display: "Satoshi", "sans-serif";
      --breakpoint-3xl: 1920px;
      --color-avocado-500: oklch(0.84 0.18 117.33);
      --ease-fluid: cubic-bezier(0.3, 0, 0, 1);
    }
    ```

- **CSS import syntax**: Use `@import "tailwindcss"` instead of `@tailwind` directives
  - Old: `@tailwind base; @tailwind components; @tailwind utilities;`
  - New: `@import "tailwindcss";`

- **Package changes**:
  - PostCSS plugin is now `@tailwindcss/postcss` (not `tailwindcss`)
  - CLI is now `@tailwindcss/cli`
  - Vite plugin is `@tailwindcss/vite`
  - No need for `postcss-import` or `autoprefixer` anymore

- **Native CSS cascade layers**: Uses real CSS `@layer` instead of Tailwind's custom implementation

## Theme Configuration

- **CSS theme variables**: All design tokens are available as CSS variables
  - Namespace format: `--category-name` (e.g., `--color-blue-500`, `--font-sans`)
  - Access in CSS: `var(--color-blue-500)`
  - Available namespaces:
    - `--color-*` : Color utilities like `bg-red-500` and `text-sky-300`
    - `--font-*` : Font family utilities like `font-sans`
    - `--text-*` : Font size utilities like `text-xl`
    - `--font-weight-*` : Font weight utilities like `font-bold`
    - `--tracking-*` : Letter spacing utilities like `tracking-wide`
    - `--leading-*` : Line height utilities like `leading-tight`
    - `--breakpoint-*` : Responsive breakpoint variants like `sm:*`
    - `--container-*` : Container query variants like `@sm:*` and size utilities like `max-w-md`
    - `--spacing-*` : Spacing and sizing utilities like `px-4` and `max-h-16`
    - `--radius-*` : Border radius utilities like `rounded-sm`
    - `--shadow-*` : Box shadow utilities like `shadow-md`
    - `--inset-shadow-*` : Inset box shadow utilities like `inset-shadow-xs`
    - `--drop-shadow-*` : Drop shadow filter utilities like `drop-shadow-md`
    - `--blur-*` : Blur filter utilities like `blur-md`
    - `--perspective-*` : Perspective utilities like `perspective-near`
    - `--aspect-*` : Aspect ratio utilities like `aspect-video`
    - `--ease-*` : Transition timing function utilities like `ease-out`
    - `--animate-*` : Animation utilities like `animate-spin`
  

- **Simplified theme configuration**: Many utilities no longer need theme configuration
  - Utilities like `grid-cols-12`, `z-40`, and `opacity-70` work without configuration
  - Data attributes like `data-selected:opacity-100` don't need configuration

- **Dynamic spacing scale**: Derived from a single spacing value
  - Default: `--spacing: 0.25rem`
  - Every multiple of the base value is available (e.g., `mt-21` works automatically)

- **Overriding theme namespaces**:
  - Override entire namespace: `--font-*: initial;`
  - Override entire theme: `--*: initial;`


## New Features

- **Container query support**: Built-in now, no plugin needed
  - `@container` for container context
  - `@sm:`, `@md:`, etc. for container-based breakpoints
  - `@max-md:` for max-width container queries
  - Combine with `@min-md:@max-xl:hidden` for ranges

- **3D transforms**:
  - `transform-3d` enables 3D transforms
  - `rotate-x-*`, `rotate-y-*`, `rotate-z-*` for 3D rotation
  - `scale-z-*` for z-axis scaling
  - `translate-z-*` for z-axis translation
  - `perspective-*` utilities (`perspective-near`, `perspective-distant`, etc.)
  - `perspective-origin-*` utilities
  - `backface-visible` and `backface-hidden`

- **Gradient enhancements**:
  - Linear gradient angles: `bg-linear-45` (renamed from `bg-gradient-*`)
  - Gradient interpolation: `bg-linear-to-r/oklch`, `bg-linear-to-r/srgb`
  - Conic and radial gradients: `bg-conic`, `bg-radial-[at_25%_25%]`

- **Shadow enhancements**:
  - `inset-shadow-*` and `inset-ring-*` utilities
  - Can be composed with regular `shadow-*` and `ring-*`

- **New CSS property utilities**:
  - `field-sizing-content` for auto-resizing textareas
  - `scheme-light`, `scheme-dark` for `color-scheme` property
  - `font-stretch-*` utilities for variable fonts

## New Variants

- **Composable variants**: Chain variants together
  - Example: `group-has-data-potato:opacity-100`

- **New variants**:
  - `starting` variant for `@starting-style` transitions
  - `not-*` variant for `:not()` pseudo-class
  - `inert` variant for `inert` attribute
  - `nth-*` variants (`nth-3:`, `nth-last-5:`, `nth-of-type-4:`, `nth-last-of-type-6:`)
  - `in-*` variant (like `group-*` but without adding `group` class)
  - `open` variant now supports `:popover-open`
  - `**` variant for targeting all descendants

## Custom Extensions

- **Custom utilities**: Use `@utility` directive
  ```css
  @utility tab-4 {
    tab-size: 4;
  }
  ```

- **Custom variants**: Use `@variant` directive
  ```css
  @variant pointer-coarse (@media (pointer: coarse));
  @variant theme-midnight (&:where([data-theme="midnight"] *));
  ```

- **Plugins**: Use `@plugin` directive
  ```css
  @plugin "@tailwindcss/typography";
  ```

## Breaking Changes

- **Removed deprecated utilities**:
  - `bg-opacity-*` → Use `bg-black/50` instead
  - `text-opacity-*` → Use `text-black/50` instead
  - And others: `border-opacity-*`, `divide-opacity-*`, etc.

- **Renamed utilities**:
  - `shadow-sm` → `shadow-xs` (and `shadow` → `shadow-sm`)
  - `drop-shadow-sm` → `drop-shadow-xs` (and `drop-shadow` → `drop-shadow-sm`)
  - `blur-sm` → `blur-xs` (and `blur` → `blur-sm`)
  - `rounded-sm` → `rounded-xs` (and `rounded` → `rounded-sm`)
  - `outline-none` → `outline-hidden` (for the old behavior)

- **Default style changes**:
  - Default border color is now `currentColor` (was `gray-200`)
  - Default `ring` width is now 1px (was 3px)
  - Placeholder text now uses current color at 50% opacity (was `gray-400`)
  - Hover styles only apply on devices that support hover (`@media (hover: hover)`)

- **Syntax changes**:
  - CSS variables in arbitrary values: `bg-(--brand-color)` instead of `bg-[--brand-color]`
  - Stacked variants now apply left-to-right (not right-to-left)
  - Use CSS variables instead of `theme()` function 

## Advanced Configuration

- **Using a prefix**:
  ```css
  @import "tailwindcss" prefix(tw);
  ```
  - Results in classes like `tw:flex`, `tw:bg-red-500`, `tw:hover:bg-red-600`

- **Source detection**:
  - Automatic by default (ignores `.gitignore` files and binary files)
  - Add sources: `@source "../node_modules/@my-company/ui-lib";`
  - Disable automatic detection: `@import "tailwindcss" source(none);`

- **Legacy config files**:
  ```css
  @import "tailwindcss";
  @config "../../tailwind.config.js";
  ```

- **Dark mode configuration**:
  ```css
  @import "tailwindcss";
  @variant dark (&:where(.dark, .dark *));
  ```

- **Container customization**: Extend with `@utility`
  ```css
  @utility container {
    margin-inline: auto;
    padding-inline: 2rem;
  }
  ```

- **Using `@apply` in Vue/Svelte**:
  ```html
  <style>
    @import "../../my-theme.css" theme(reference);
    /* or */
    @import "tailwindcss/theme" theme(reference);
    
    h1 {
      @apply font-bold text-2xl text-red-500;
    }
  </style>
  ```