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Chapter 6: Styling and CSS in Next.js

What is Styling in Next.js?​

Next.js provides multiple approaches for styling your applications, from traditional CSS to modern CSS-in-JS solutions. The framework supports various styling methods while maintaining excellent performance and developer experience.

Available Styling Options:

  • Global CSS: Traditional CSS files for global styles
  • CSS Modules: Scoped CSS with automatic class name generation
  • Styled JSX: CSS-in-JS solution built into Next.js
  • Sass/SCSS: Enhanced CSS with variables and mixins
  • CSS-in-JS Libraries: Styled-components, Emotion, and others
  • Utility-First CSS: Tailwind CSS and similar frameworks

Why Choose Different Styling Approaches?​

Global CSS:

  • Simple and familiar
  • Good for reset styles and global variables
  • Easy to integrate with existing CSS

CSS Modules:

  • Scoped styles prevent conflicts
  • Automatic class name generation
  • Great for component-specific styles

Styled JSX:

  • Built into Next.js
  • No additional dependencies
  • Dynamic styling with JavaScript

Sass/SCSS:

  • Enhanced CSS features
  • Variables, mixins, and functions
  • Better organization for large projects

CSS-in-JS:

  • Dynamic styling based on props
  • Type safety with TypeScript
  • Component-scoped styles

How to Implement Different Styling Methods​

1. Global CSS​

Setting up Global Styles:

/* styles/globals.css */
html,
body {
  padding: 0;
  margin: 0;
  font-family: -apple-system, BlinkMacSystemFont, Segoe UI, Roboto, Oxygen,
    Ubuntu, Cantarell, Fira Sans, Droid Sans, Helvetica Neue, sans-serif;
  line-height: 1.6;
  color: #333;
}

* {
  box-sizing: border-box;
}

a {
  color: #0070f3;
  text-decoration: none;
}

a:hover {
  text-decoration: underline;
}

img {
  max-width: 100%;
  height: auto;
}

/* CSS Variables */
:root {
  --primary-color: #0070f3;
  --secondary-color: #f0f0f0;
  --text-color: #333;
  --background-color: #fff;
  --border-radius: 4px;
  --spacing-unit: 8px;
}

/* Dark mode support */
@media (prefers-color-scheme: dark) {
  :root {
    --text-color: #fff;
    --background-color: #000;
    --secondary-color: #1a1a1a;
  }
}

Importing Global Styles:

// pages/_app.js
import '../styles/globals.css'

export default function MyApp({ Component, pageProps }) {
  return <Component {...pageProps} />
}

2. CSS Modules​

Creating CSS Modules:

/* components/Button.module.css */
.button {
  padding: 12px 24px;
  border: none;
  border-radius: var(--border-radius);
  cursor: pointer;
  font-size: 16px;
  font-weight: 500;
  transition: all 0.2s ease;
  display: inline-flex;
  align-items: center;
  justify-content: center;
  text-decoration: none;
}

.primary {
  background-color: var(--primary-color);
  color: white;
}

.primary:hover {
  background-color: #0051cc;
  transform: translateY(-1px);
}

.secondary {
  background-color: var(--secondary-color);
  color: var(--text-color);
}

.secondary:hover {
  background-color: #e0e0e0;
}

.large {
  padding: 16px 32px;
  font-size: 18px;
}

.small {
  padding: 8px 16px;
  font-size: 14px;
}

.disabled {
  opacity: 0.6;
  cursor: not-allowed;
}

.disabled:hover {
  transform: none;
}

Using CSS Modules:

// components/Button.js
import styles from './Button.module.css'
import { clsx } from 'clsx'

export default function Button({ 
  children, 
  variant = 'primary', 
  size = 'medium',
  disabled = false,
  className,
  ...props 
}) {
  const buttonClasses = clsx(
    styles.button,
    styles[variant],
    styles[size],
    {
      [styles.disabled]: disabled,
    },
    className
  )

  return (
    <button 
      className={buttonClasses}
      disabled={disabled}
      {...props}
    >
      {children}
    </button>
  )
}

3. Styled JSX​

Basic Styled JSX:

// components/Card.js
export default function Card({ title, children, variant = 'default' }) {
  return (
    <div className="card">
      <h3 className="title">{title}</h3>
      <div className="content">{children}</div>
      
      <style jsx>{`
        .card {
          background: white;
          border-radius: 8px;
          box-shadow: 0 2px 8px rgba(0, 0, 0, 0.1);
          padding: 24px;
          margin: 16px 0;
          transition: box-shadow 0.2s ease;
        }
        
        .card:hover {
          box-shadow: 0 4px 16px rgba(0, 0, 0, 0.15);
        }
        
        .title {
          margin: 0 0 16px 0;
          color: #333;
          font-size: 1.5rem;
          font-weight: 600;
        }
        
        .content {
          color: #666;
          line-height: 1.6;
        }
      `}</style>
    </div>
  )
}

Dynamic Styled JSX:

// components/ProgressBar.js
export default function ProgressBar({ progress, color = '#0070f3' }) {
  return (
    <div className="progress-container">
      <div className="progress-bar">
        <div className="progress-fill" />
      </div>
      <span className="progress-text">{progress}%</span>
      
      <style jsx>{`
        .progress-container {
          display: flex;
          align-items: center;
          gap: 12px;
        }
        
        .progress-bar {
          flex: 1;
          height: 8px;
          background-color: #f0f0f0;
          border-radius: 4px;
          overflow: hidden;
        }
        
        .progress-fill {
          height: 100%;
          width: ${progress}%;
          background-color: ${color};
          transition: width 0.3s ease;
        }
        
        .progress-text {
          font-size: 14px;
          font-weight: 500;
          color: #666;
          min-width: 40px;
        }
      `}</style>
    </div>
  )
}

Global Styled JSX:

// components/GlobalStyles.js
export default function GlobalStyles() {
  return (
    <style jsx global>{`
      body {
        font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, sans-serif;
        line-height: 1.6;
        color: #333;
      }
      
      h1, h2, h3, h4, h5, h6 {
        margin: 0 0 1rem 0;
        font-weight: 600;
        line-height: 1.2;
      }
      
      p {
        margin: 0 0 1rem 0;
      }
      
      .container {
        max-width: 1200px;
        margin: 0 auto;
        padding: 0 20px;
      }
    `}</style>
  )
}

4. Sass/SCSS Support​

Installing Sass:

npm install sass

SCSS Variables and Mixins:

// styles/variables.scss
$primary-color: #0070f3;
$secondary-color: #f0f0f0;
$text-color: #333;
$background-color: #fff;
$border-radius: 4px;
$spacing-unit: 8px;

// Breakpoints
$mobile: 768px;
$tablet: 1024px;
$desktop: 1200px;

// Mixins
@mixin flex-center {
  display: flex;
  align-items: center;
  justify-content: center;
}

@mixin button-base {
  padding: 12px 24px;
  border: none;
  border-radius: $border-radius;
  cursor: pointer;
  font-size: 16px;
  transition: all 0.2s ease;
}

@mixin responsive($breakpoint) {
  @if $breakpoint == mobile {
    @media (max-width: $mobile) {
      @content;
    }
  }
  @if $breakpoint == tablet {
    @media (max-width: $tablet) {
      @content;
    }
  }
  @if $breakpoint == desktop {
    @media (min-width: $desktop) {
      @content;
    }
  }
}

Using SCSS in Components:

// components/Header.module.scss
@import '../styles/variables.scss';

.header {
  background: $background-color;
  border-bottom: 1px solid $secondary-color;
  padding: $spacing-unit * 2;
  
  @include flex-center;
  justify-content: space-between;
  
  @include responsive(mobile) {
    padding: $spacing-unit;
    flex-direction: column;
    gap: $spacing-unit;
  }
}

.logo {
  font-size: 1.5rem;
  font-weight: 700;
  color: $primary-color;
  text-decoration: none;
}

.nav {
  display: flex;
  gap: $spacing-unit * 3;
  
  @include responsive(mobile) {
    gap: $spacing-unit * 2;
  }
}

.navLink {
  color: $text-color;
  text-decoration: none;
  font-weight: 500;
  transition: color 0.2s ease;
  
  &:hover {
    color: $primary-color;
  }
  
  &.active {
    color: $primary-color;
    font-weight: 600;
  }
}

5. Tailwind CSS Integration​

Installing Tailwind CSS:

npm install -D tailwindcss postcss autoprefixer
npx tailwindcss init -p

Tailwind Configuration:

// tailwind.config.js
/** @type {import('tailwindcss').Config} */
module.exports = {
  content: [
    './pages/**/*.{js,ts,jsx,tsx,mdx}',
    './components/**/*.{js,ts,jsx,tsx,mdx}',
    './app/**/*.{js,ts,jsx,tsx,mdx}',
  ],
  theme: {
    extend: {
      colors: {
        primary: {
          50: '#eff6ff',
          500: '#3b82f6',
          900: '#1e3a8a',
        },
      },
      fontFamily: {
        sans: ['Inter', 'system-ui', 'sans-serif'],
      },
    },
  },
  plugins: [],
}

Using Tailwind CSS:

// components/TailwindCard.js
export default function TailwindCard({ title, children, variant = 'default' }) {
  const baseClasses = "bg-white rounded-lg shadow-md p-6 transition-shadow duration-200"
  const variantClasses = {
    default: "hover:shadow-lg",
    primary: "bg-primary-50 border-l-4 border-primary-500",
    success: "bg-green-50 border-l-4 border-green-500",
  }

  return (
    <div className={`${baseClasses} ${variantClasses[variant]}`}>
      <h3 className="text-xl font-semibold text-gray-900 mb-4">{title}</h3>
      <div className="text-gray-600">{children}</div>
    </div>
  )
}

6. CSS-in-JS with Styled Components​

Installing Styled Components:

npm install styled-components
npm install -D babel-plugin-styled-components

Babel Configuration:

// .babelrc
{
  "presets": ["next/babel"],
  "plugins": [
    [
      "babel-plugin-styled-components",
      {
        "ssr": true,
        "displayName": true
      }
    ]
  ]
}

Using Styled Components:

// components/StyledButton.js
import styled, { css } from 'styled-components'

const Button = styled.button`
  padding: 12px 24px;
  border: none;
  border-radius: 4px;
  cursor: pointer;
  font-size: 16px;
  font-weight: 500;
  transition: all 0.2s ease;
  display: inline-flex;
  align-items: center;
  justify-content: center;
  
  ${props => props.variant === 'primary' && css`
    background-color: #0070f3;
    color: white;
    
    &:hover {
      background-color: #0051cc;
      transform: translateY(-1px);
    }
  `}
  
  ${props => props.variant === 'secondary' && css`
    background-color: #f0f0f0;
    color: #333;
    
    &:hover {
      background-color: #e0e0e0;
    }
  `}
  
  ${props => props.size === 'large' && css`
    padding: 16px 32px;
    font-size: 18px;
  `}
  
  ${props => props.size === 'small' && css`
    padding: 8px 16px;
    font-size: 14px;
  `}
  
  ${props => props.disabled && css`
    opacity: 0.6;
    cursor: not-allowed;
    
    &:hover {
      transform: none;
    }
  `}
`

export default function StyledButton({ children, ...props }) {
  return <Button {...props}>{children}</Button>
}

Advanced Styling Techniques​

1. CSS Custom Properties (CSS Variables)​

/* styles/globals.css */
:root {
  --primary-color: #0070f3;
  --secondary-color: #f0f0f0;
  --text-color: #333;
  --background-color: #fff;
  --border-radius: 4px;
  --spacing-unit: 8px;
  --font-size-base: 16px;
  --font-size-lg: 18px;
  --font-size-sm: 14px;
  --shadow-sm: 0 1px 2px rgba(0, 0, 0, 0.05);
  --shadow-md: 0 4px 6px rgba(0, 0, 0, 0.1);
  --shadow-lg: 0 10px 15px rgba(0, 0, 0, 0.1);
}

/* Dark mode */
[data-theme="dark"] {
  --text-color: #fff;
  --background-color: #000;
  --secondary-color: #1a1a1a;
}
// components/ThemeProvider.js
import { createContext, useContext, useEffect, useState } from 'react'

const ThemeContext = createContext()

export function ThemeProvider({ children }) {
  const [theme, setTheme] = useState('light')

  useEffect(() => {
    const savedTheme = localStorage.getItem('theme')
    if (savedTheme) {
      setTheme(savedTheme)
    }
  }, [])

  useEffect(() => {
    document.documentElement.setAttribute('data-theme', theme)
    localStorage.setItem('theme', theme)
  }, [theme])

  const toggleTheme = () => {
    setTheme(prev => prev === 'light' ? 'dark' : 'light')
  }

  return (
    <ThemeContext.Provider value={{ theme, toggleTheme }}>
      {children}
    </ThemeContext.Provider>
  )
}

export const useTheme = () => useContext(ThemeContext)

2. Responsive Design​

/* styles/responsive.css */
.container {
  max-width: 1200px;
  margin: 0 auto;
  padding: 0 20px;
}

.grid {
  display: grid;
  gap: 20px;
  grid-template-columns: repeat(auto-fit, minmax(300px, 1fr));
}

/* Mobile First Approach */
@media (min-width: 768px) {
  .container {
    padding: 0 40px;
  }
  
  .grid {
    grid-template-columns: repeat(2, 1fr);
  }
}

@media (min-width: 1024px) {
  .grid {
    grid-template-columns: repeat(3, 1fr);
  }
}

@media (min-width: 1200px) {
  .container {
    padding: 0 60px;
  }
}

3. Animation and Transitions​

/* styles/animations.css */
@keyframes fadeIn {
  from {
    opacity: 0;
    transform: translateY(20px);
  }
  to {
    opacity: 1;
    transform: translateY(0);
  }
}

@keyframes slideIn {
  from {
    transform: translateX(-100%);
  }
  to {
    transform: translateX(0);
  }
}

.fade-in {
  animation: fadeIn 0.5s ease-out;
}

.slide-in {
  animation: slideIn 0.3s ease-out;
}

.hover-lift {
  transition: transform 0.2s ease;
}

.hover-lift:hover {
  transform: translateY(-2px);
}

Best Practices​

1. CSS Organization​

/* ✅ Good: Organized CSS structure */
/* 1. Reset and base styles */
/* 2. Variables and mixins */
/* 3. Layout styles */
/* 4. Component styles */
/* 5. Utility classes */
/* 6. Media queries */

2. Performance Optimization​

// ✅ Good: Lazy load CSS
import dynamic from 'next/dynamic'

const HeavyComponent = dynamic(() => import('./HeavyComponent'), {
  loading: () => <div>Loading...</div>,
  ssr: false
})

3. CSS-in-JS Best Practices​

// ✅ Good: Memoized styled components
import { memo } from 'react'
import styled from 'styled-components'

const StyledButton = styled.button`
  /* styles */
`

export default memo(StyledButton)

Common Mistakes to Avoid​

1. CSS Specificity Issues​

/* ❌ Wrong: High specificity */
div.container .content .text {
  color: red;
}

/* ✅ Correct: Lower specificity */
.text {
  color: red;
}

2. Inline Styles Overuse​

// ❌ Wrong: Too many inline styles
<div style={{ color: 'red', fontSize: '16px', margin: '10px' }}>

// ✅ Correct: Use CSS classes
<div className="text-red text-base m-2">

3. Missing CSS Reset​

/* ❌ Wrong: No CSS reset */
/* Browser default styles cause inconsistencies */

/* ✅ Correct: Include CSS reset */
* {
  margin: 0;
  padding: 0;
  box-sizing: border-box;
}

Summary​

Next.js provides flexible styling options to suit different project needs:

  • Global CSS for base styles and variables
  • CSS Modules for component-scoped styles
  • Styled JSX for dynamic styling
  • Sass/SCSS for enhanced CSS features
  • CSS-in-JS for component-based styling
  • Utility frameworks like Tailwind for rapid development

Key Takeaways:

  • Choose the right styling approach for your project
  • Use CSS variables for theming and consistency
  • Implement responsive design from the start
  • Optimize for performance with code splitting
  • Follow consistent naming conventions

This tutorial is part of the comprehensive Next.js learning path at syscook.dev. Continue to the next chapter to learn about data fetching and API integration.

Author: syscook.dev
Last Updated: December 2024