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# Tailwind CSS Development

## Package Licensing

Before proposing, installing, or integrating any additional package, verify that its license permits commercial use. If the license is non-commercial, unclear, or otherwise incompatible with commercial projects, do not use that package and clearly tell the user that we need to build the feature ourselves or choose a commercially permitted alternative.

## Documentation

Use `search-docs` for detailed Tailwind CSS v4 patterns and documentation.

## Basic Usage

- Use Tailwind CSS classes to style HTML. Check and follow existing Tailwind conventions in the project before introducing new patterns.
- Offer to extract repeated patterns into components that match the project's conventions (e.g., Blade, JSX, Vue).
- Consider class placement, order, priority, and defaults. Remove redundant classes, add classes to parent or child elements carefully to reduce repetition, and group elements logically.

## Tailwind CSS v4 Specifics

- Always use Tailwind CSS v4 and avoid deprecated utilities.
- `corePlugins` is not supported in Tailwind v4.

### CSS-First Configuration

In Tailwind v4, configuration is CSS-first using the `@theme` directive — no separate `tailwind.config.js` file is needed:

<!-- CSS-First Config -->
```css
@theme {
  --color-brand: oklch(0.72 0.11 178);
}
```

### Import Syntax

In Tailwind v4, import Tailwind with a regular CSS `@import` statement instead of the `@tailwind` directives used in v3:

<!-- v4 Import Syntax -->
```diff
- @tailwind base;
- @tailwind components;
- @tailwind utilities;
+ @import "tailwindcss";
```

### Replaced Utilities

Tailwind v4 removed deprecated utilities. Use the replacements shown below. Opacity values remain numeric.

| Deprecated | Replacement |
|------------|-------------|
| bg-opacity-* | bg-black/* |
| text-opacity-* | text-black/* |
| border-opacity-* | border-black/* |
| divide-opacity-* | divide-black/* |
| ring-opacity-* | ring-black/* |
| placeholder-opacity-* | placeholder-black/* |
| flex-shrink-* | shrink-* |
| flex-grow-* | grow-* |
| overflow-ellipsis | text-ellipsis |
| decoration-slice | box-decoration-slice |
| decoration-clone | box-decoration-clone |

## Spacing

Use `gap` utilities instead of margins for spacing between siblings:

<!-- Gap Utilities -->
```html
<div class="flex gap-8">
    <div>Item 1</div>
    <div>Item 2</div>
</div>
```

## Dark Mode

If existing pages and components support dark mode, new pages and components must support it the same way, typically using the `dark:` variant:

<!-- Dark Mode -->
```html
<div class="bg-white dark:bg-gray-900 text-gray-900 dark:text-white">
    Content adapts to color scheme
</div>
```

## Common Patterns

### Flexbox Layout

<!-- Flexbox Layout -->
```html
<div class="flex items-center justify-between gap-4">
    <div>Left content</div>
    <div>Right content</div>
</div>
```

### Grid Layout

<!-- Grid Layout -->
```html
<div class="grid grid-cols-1 md:grid-cols-2 lg:grid-cols-3 gap-6">
    <div>Card 1</div>
    <div>Card 2</div>
    <div>Card 3</div>
</div>
```

## Common Pitfalls

- Using deprecated v3 utilities (bg-opacity-*, flex-shrink-*, etc.)
- Using `@tailwind` directives instead of `@import "tailwindcss"`
- Trying to use `tailwind.config.js` instead of CSS `@theme` directive
- Using margins for spacing between siblings instead of gap utilities
- Forgetting to add dark mode variants when the project uses dark mode