Tailwind CSS v4

Expert guidance for Tailwind CSS v4, CSS-first configuration, modern utility patterns, and type-safe component styling with tailwind-variants.

CSS-First Configuration

Tailwind CSS v4 eliminates

tailwind.config.ts

in favor of CSS-only configuration. All configuration lives in CSS files using special directives.

Core Directives:

```
@import "tailwindcss"
```
- Entry point that loads Tailwind
```
@theme { }
```
- Define or extend design tokens
```
@theme static { }
```
- Define tokens that should not generate utilities
```
@utility
```
- Create custom utilities
```
@custom-variant
```
- Define custom variants

Minimal Example:

css

@import "tailwindcss";

@theme {
  --color-brand: oklch(0.72 0.11 178);
  --font-display: "Inter", sans-serif;
  --spacing-edge: 1.5rem;
}

All theme tokens defined with

@theme

automatically become available as utility classes. For example,

--color-brand

can be used as

bg-brand

text-brand

border-brand

, etc.

ESLint Integration

Use

eslint-plugin-better-tailwindcss

for Tailwind CSS v4 class validation and style enforcement.

Correctness Rules (errors):

```
no-conflicting-classes
```
- Detect classes that override each other
```
no-unknown-classes
```
- Flag classes not registered with Tailwind

Stylistic Rules (warnings):

```
enforce-canonical-classes
```
- Use standard v4 class names
```
enforce-shorthand-classes
```
- Use abbreviated class versions
```
no-deprecated-classes
```
- Remove outdated class names
```
no-duplicate-classes
```
- Eliminate redundant declarations
```
no-unnecessary-whitespace
```
- Clean up extra spacing

Examples:

typescript

// ❌ Bad: separate padding
<div className="px-6 py-6">

// ✅ Good: shorthand
<div className="p-6">

typescript

// ❌ Bad: separate width/height
<div className="w-6 h-6">

// ✅ Good: size utility
<div className="size-6">

Run the project's ESLint check after modifying Tailwind classes to validate all changes across the codebase.

Coding Preferences

Layout and Spacing

Use
gap
for flex/grid spacing, not
space-x
/
space-y
:

The

gap

utilities handle wrapping correctly, while

space-*

utilities break when flex/grid items wrap to multiple lines.

typescript

// ✅ Good: gap handles wrapping
<div className="flex gap-4">

// ❌ Bad: breaks when items wrap
<div className="flex space-x-4">

Prefer
size-*
over separate
w-*
/
h-*
for equal dimensions:

typescript

// ✅ Good: concise
<div className="size-16">

// ❌ Bad: redundant
<div className="w-16 h-16">

Always use
min-h-dvh
instead of
min-h-screen
:

Dynamic viewport height (

dvh

) accounts for mobile browser chrome, while

vh

units ignore it and cause layout issues on mobile Safari.

typescript

// ✅ Good: works on mobile Safari
<main className="min-h-dvh">

// ❌ Bad: buggy on mobile Safari
<main className="min-h-screen">

Prefer top/left margins over bottom/right:

Consistent directionality improves layout predictability.

typescript

// ✅ Good: top margin
<div className="mt-4">

// ❌ Avoid: bottom margin (unless needed)
<div className="mb-4">

Use padding on parent containers instead of bottom margins on last child:

Padding provides consistent spacing without needing

:last-child

selectors.

typescript

// ✅ Good: padding on parent
<section className="pb-8">
  <div>Item 1</div>
  <div>Item 2</div>
  <div>Item 3</div>
</section>

// ❌ Avoid: margin on children
<section>
  <div className="mb-4">Item 1</div>
  <div className="mb-4">Item 2</div>
  <div>Item 3</div>
</section>

For max-widths, prefer container scale over pixel values:

typescript

// ✅ Good: semantic container size
<div className="max-w-2xl">

// ❌ Avoid: arbitrary pixel value
<div className="max-w-[672px]">

Typography

Avoid
leading-*
classes; use line height modifiers:

Tailwind v4 supports inline line height modifiers with the

text-{size}/{leading}

syntax.

typescript

// ✅ Good: combined size and line height
<p className="text-base/7">

// ❌ Bad: separate utilities
<p className="text-base leading-7">

Font Size Reference:

Class	Size
`text-xs`	12px
`text-sm`	14px
`text-base`	16px
`text-lg`	18px
`text-xl`	20px

Colors and Opacity

Use opacity modifier syntax, not separate opacity utilities:

All

*-opacity-*

utilities were removed in Tailwind v4. Use the modifier syntax instead.

typescript

// ✅ Good: opacity modifier
<div className="bg-red-500/60">

// ❌ Bad: removed in v4
<div className="bg-red-500 bg-opacity-60">

Prefer design tokens over arbitrary hex values:

Check the project's

@theme

configuration before using arbitrary color values.

typescript

// ✅ Good: theme token
<div className="bg-brand">

// ❌ Avoid: arbitrary hex (check theme first)
<div className="bg-[#4f46e5]">

Border Radius

Tailwind v4 renamed border radius utilities:

v3	v4 (equivalent)	Size
`rounded-sm`	`rounded-xs`	2px
`rounded`	`rounded-sm`	4px
`rounded-md`	`rounded`	6px
`rounded-lg`	`rounded-md`	8px

Use the v4 names when writing new code.

Gradients

Tailwind v4 renamed gradient utilities and added new gradient types.

Use
bg-linear-*
, not
bg-gradient-*
:

typescript

// ✅ Good: v4 syntax
<div className="bg-linear-to-r from-blue-500 to-purple-500">

// ❌ Bad: removed in v4
<div className="bg-gradient-to-r from-blue-500 to-purple-500">

New gradient types:

```
bg-radial
```
- Radial gradients
```
bg-conic
```
- Conic gradients

Example:

typescript

<div className="bg-radial from-blue-500 to-purple-500">
<div className="bg-conic from-red-500 via-yellow-500 to-green-500">

Arbitrary Values

Always prefer Tailwind's predefined scale:

Check the project's

@theme

configuration for available tokens before using arbitrary values.

typescript

// ✅ Good: predefined scale
<div className="ml-4">

// ❌ Avoid: arbitrary pixel value
<div className="ml-[16px]">

General rule: Prefer sizing scale over pixel values. Three similar lines of code is better than a premature abstraction.

Class Merging

The common pattern is a

cn

utility combining

clsx

tailwind-merge

Use
cn
for:

Static constants:
```
const CARD_BASE = cn("fixed classes")
```
Conditional classes:
```
cn("base", condition && "conditional")
```
Dynamic merging:
```
cn(baseClasses, className)
```
Conflict resolution:
```
cn("p-4", "p-6")
```
→
```
"p-6"
```

Do NOT use
cn
for:

Static strings in
```
className
```
attributes:
```
className="fixed classes"
```

Examples:

typescript

// ✅ Good: static string in className
<button className="rounded-lg px-4 py-2 font-medium bg-blue-600">

// ✅ Good: static constant with cn
const CARD_BASE = cn("rounded-lg border border-gray-300 p-4");
<div className={CARD_BASE} />

// ✅ Good: conditional with cn
<button className={cn(
  "rounded-lg px-4 py-2 font-medium",
  isActive ? "bg-blue-600" : "bg-gray-700",
  disabled && "opacity-50"
)} />

// ❌ Bad: unnecessary cn for static className attribute
<button className={cn("rounded-lg px-4 py-2 font-medium")} />

Image Sizing

Use Tailwind size classes instead of pixel values for

Image

components.

typescript

// ✅ Good: Tailwind units
<Image src={src} alt={alt} className="size-16" />
<Image src={src} alt={alt} className="w-24 h-auto" />

// ❌ Bad: pixel values
<Image src={src} alt={alt} width={64} height={64} />

Z-Index

Define z-index values as CSS custom properties in

@theme

, then reference them with the

z-(--z-*)

syntax.

Never use arbitrary z-index numbers:

typescript

// ✅ Good: theme z-index value
<div className="z-(--z-modal)">
<div className="z-(--z-sticky)">

// ❌ Bad: arbitrary z-index numbers
<div className="z-[100]">
<div className="z-[9999]">

Define z-index tokens in CSS:

css

@theme {
  --z-base: 0;
  --z-sticky: 10;
  --z-modal: 100;
  --z-tooltip: 1000;
}

Dark Mode

Use the plain

dark:

variant for dark mode styles.

Pattern:

Write light mode styles first, then add dark mode overrides.

typescript

// ✅ Good: light mode first, then dark override
<div className="bg-white text-gray-900 dark:bg-gray-900 dark:text-white">

// ❌ Avoid: dark mode first (less readable)
<div className="dark:bg-gray-900 dark:text-white bg-white text-gray-900">

CSS Modules

Use CSS Modules only as a last resort for complex CSS that cannot be easily written with Tailwind classes.

All

.module.css

files must include

@reference "#tailwind";

at the top to enable Tailwind utilities and theme tokens inside the module.

Example:

css

/* component.module.css */
@reference "#tailwind";

.component {
  /* Complex CSS that can't be expressed with Tailwind utilities */
  /* Can still use Tailwind utilities and theme tokens */
}

Common Tasks

Adding a Component with Variants

Read
```
references/tailwind-variants.md
```
for patterns
Check the project's
```
@theme
```
configuration for available tokens
Use
```
tv()
```
from
```
tailwind-variants
```
for type-safe variants

Example:

typescript

import { tv } from "tailwind-variants";

const button = tv({
  base: "rounded-lg px-4 py-2 font-medium",
  variants: {
    color: {
      primary: "bg-blue-600 text-white",
      secondary: "bg-gray-600 text-white",
    },
    size: {
      sm: "text-sm",
      md: "text-base",
      lg: "text-lg",
    },
  },
});

Debugging Styles

Check
```
references/tailwind-v4-rules.md
```
for breaking changes
Verify gradient syntax (
```
bg-linear-*
```
, not
```
bg-gradient-*
```
)
Verify CSS variable syntax (
```
bg-my-color
```
, not
```
bg-[--var-my-color]
```
)
Check if arbitrary value exists in the project's
```
@theme
```
configuration

Working with Colors

Check the project's
```
@theme
```
configuration first to see available colors
Use semantic color names when available
Use opacity modifiers for transparency (
```
/20
```
,
```
/50
```
, etc.)
Avoid arbitrary colors unless absolutely necessary

Example:

typescript

// ✅ Good: theme token with opacity
<div className="bg-brand/20 text-brand">

// ❌ Avoid: arbitrary hex
<div className="bg-[#4f46e5]/20 text-[#4f46e5]">

Adding Animations

Read
```
references/tw-animate-css.md
```
for available animations
Combine a base class (
```
animate-in
```
or
```
animate-out
```
) with effect classes
Note decimal spacing gotcha: use
```
[0.625rem]
```
syntax, not
```
2.5
```

Example:

typescript

// Enter: fade + slide up
<div className="fade-in slide-in-from-bottom-4 duration-300 animate-in">

// Exit: fade + slide down
<div className="fade-out slide-out-to-bottom-4 duration-200 animate-out">

Quick Reference Table

Aspect	Pattern
Configuration	CSS-only: `@theme` , `@utility` , `@custom-variant`
Gradients	`bg-linear-*` , `bg-radial` , `bg-conic`
Opacity	Modifier syntax: `bg-black/50`
Line Height	Modifier syntax: `text-base/7`
CSS Variables	`bg-my-color` (auto-created from `@theme` )
CSS Modules	`@reference "#tailwind";` at top
Class Merging	`cn()` for conditionals; plain string for static
Viewport	`min-h-dvh` (not `min-h-screen` )
Component Variants	`references/tailwind-variants.md`
Animations	`references/tw-animate-css.md`
V4 Rules	`references/tailwind-v4-rules.md`

Reference Documentation

Tailwind v4 Rules & Best Practices:
```
references/tailwind-v4-rules.md
```
— Breaking changes, removed/renamed utilities, layout rules, typography, gradients, CSS variables, new v4 features, common pitfalls
tailwind-variants Patterns:
```
references/tailwind-variants.md
```
— Component variants, slots API, composition, TypeScript integration, responsive variants
tw-animate-css Reference:
```
references/tw-animate-css.md
```
— Enter/exit animations, slide/fade/zoom utilities, spacing gotchas

tailwind-css

NPX Install

Tags

SKILL.md Content

Tailwind CSS v4

CSS-First Configuration

ESLint Integration

Coding Preferences

Layout and Spacing

Typography

Colors and Opacity

Border Radius

Gradients

Arbitrary Values

Class Merging

Image Sizing

Z-Index

Dark Mode

CSS Modules

Common Tasks

Adding a Component with Variants

Debugging Styles

Working with Colors

Adding Animations

Quick Reference Table

Reference Documentation