CSS Inliner

Bidirectional CSS-HTML converter with smart selector generation

Convert between CSS and inline styles effortlessly. Perfect for email templates, production optimization, and development workflows.

🚀 Features

Forward Conversion (CSS → Inline)

• ✅ Full CSS selector support - element, class, descendant, compound selectors
• ✅ Preserve responsive styles - @media, @import, @keyframes, @font-face
• ✅ Keep pseudo-classes - :hover, :focus, :active in <style> tags
• ✅ Smart style merging - respects CSS specificity and existing inline styles

Reverse Conversion (Inline → CSS)

• ✅ Smart selector generation - uses existing classes, creates nested selectors
• ✅ Style deduplication - groups identical styles under combined selectors
• ✅ Minimal HTML changes - prioritizes existing structure over auto-classes
• ✅ Two output modes - internal <style> tag or external CSS file

📦 Installation

npm install css-inliner
# or
pnpm add css-inliner
# or
yarn add css-inliner

🎯 Quick Start

Forward: CSS to Inline Styles

import { inlineCSS } from 'css-inliner';

const html = `
<style>
  .header { color: blue; font-size: 24px; }
  .header:hover { color: darkblue; }
</style>
<div class="header">Hello World</div>
`;

const result = await inlineCSS(html);
console.log(result);
// Output:
// <style>.header:hover { color: darkblue; }</style>
// <div class="header" style="color:blue;font-size:24px">Hello World</div>

Reverse: Inline Styles to CSS (Internal)

import { reverseCSSInternal } from 'css-inliner';

const html = `
<div class="header" style="color:blue;font-size:24px">Hello</div>
<div class="header" style="color:blue;font-size:24px">World</div>
`;

const result = await reverseCSSInternal(html);
console.log(result);
// Output:
// <style>
// .header { color:blue; font-size:24px; }
// </style>
// <div class="header">Hello</div>
// <div class="header">World</div>

Reverse: Inline Styles to External CSS

import { reverseCSSExternal } from 'css-inliner';
import { writeFileSync } from 'fs';

const html = `
<div class="nav" style="display:flex;gap:20px">Navigation</div>
`;

const { html: htmlOutput, css: cssOutput } = await reverseCSSExternal(html);

writeFileSync('index.html', htmlOutput);
writeFileSync('styles.css', cssOutput);

// index.html:
// <link rel="stylesheet" href="styles.css">
// <div class="nav">Navigation</div>

// styles.css:
// .nav { display:flex; gap:20px; }

📚 API Reference

inlineCSS(input: string): Promise<string>

Converts CSS rules to inline styles.

Parameters:

• input - HTML string or URL

Returns: HTML string with inlined CSS

Features:

• Inlines all CSS rules into element style attributes
• Preserves @media, @import, @keyframes, @font-face in <style> tag
• Keeps pseudo-classes (:hover, :focus) in <style> tag
• Respects CSS specificity
• Merges with existing inline styles

---

reverseCSSInternal(input: string): Promise<string>

Extracts inline styles to internal CSS (<style> tag).

Parameters:

• input - HTML string or URL

Returns: HTML string with CSS in <style> tag

Smart Selector Strategy:

1. Use existing classes - .header, .nav-list
2. Create nested selectors - .parent .child, .nav a
3. Use element selectors - body, html, h1
4. Auto-generate only when needed - .auto-style-1, .auto-style-2

Features:

• Deduplicates identical styles
• Preserves existing CSS (@media, :hover, etc.)
• Minimal HTML modifications
• Clean, semantic CSS output

---

reverseCSSExternal(input: string): Promise<{html: string, css: string}>

Extracts inline styles to external CSS file.

Parameters:

• input - HTML string or URL

Returns: Object with html and css strings

Use Case: Production websites that benefit from browser caching

const { html, css } = await reverseCSSExternal(inlinedHTML);
// html: contains <link rel="stylesheet" href="styles.css">
// css: all extracted CSS rules

🎨 Use Cases

Email Templates

// Convert CSS to inline for email clients
const emailHTML = await inlineCSS(template);
sendEmail(emailHTML);

Production Optimization

// Extract inline CSS to cacheable file
const { html, css } = await reverseCSSExternal(buildOutput);
writeFileSync('index.html', html);
writeFileSync('styles.css', css);

Development Workflow

// Convert messy inline styles to readable CSS
const readable = await reverseCSSInternal(legacyHTML);

Round-Trip Conversion

// Chain conversions for different outputs
const inlined = await inlineCSS(original);
const withStyleTag = await reverseCSSInternal(inlined);
const { html, css } = await reverseCSSExternal(withStyleTag);

🔧 Advanced Examples

Responsive Design

const html = `
<style>
  .container { max-width: 1200px; }
  @media (max-width: 768px) {
    .container { max-width: 100%; }
  }
</style>
<div class="container">Content</div>
`;

const result = await inlineCSS(html);
// @media queries are preserved in <style> tag
// Regular styles are inlined

Font Imports

const html = `
<style>
  @import url('https://fonts.googleapis.com/css2?family=Roboto');
  body { font-family: 'Roboto', sans-serif; }
</style>
<body>Text</body>
`;

const result = await inlineCSS(html);
// @import is preserved
// font-family is inlined with proper quote escaping

Nested Selectors

const html = `
<div class="nav">
  <a style="color:blue;text-decoration:none">Link 1</a>
  <a style="color:blue;text-decoration:none">Link 2</a>
</div>
`;

const result = await reverseCSSInternal(html);
// Output:
// <style>
// .nav a { color:blue; text-decoration:none; }
// </style>
// <div class="nav">
//   <a>Link 1</a>
//   <a>Link 2</a>
// </div>

📊 Performance

• Fast parsing - Uses optimized CSS and HTML parsers
• Minimal overhead - Efficient DOM traversal and style matching
• Memory efficient - Streaming-friendly architecture

🧪 Testing

# Run tests
pnpm test

# Watch mode
pnpm test:watch

# Coverage
pnpm test:coverage

🤝 Contributing

Contributions are welcome! Please feel free to submit a Pull Request.

📄 License

MIT © Osman Beyhan

🙏 Acknowledgments

Built with:

• css-tree - CSS parser
• htmlparser2 - HTML parser
• dom-serializer - DOM to HTML

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Made with ❤️ for developers who work with HTML and CSS