Modern CSS is a comprehensive reference project created by Naeem Noor that offers over 98 side-by-side comparisons of outdated CSS hacks alongside their modern, native web platform replacements. The site acts as a practical guide for developers to modernize their workflows by phasing out legacy techniques like clearfix hacks, absolute positioning workarounds, and heavy reliance on JavaScript for styling or layout logic. By highlighting native capabilities like CSS Grid, container queries, cascade layers, and custom properties, the project empowers developers to write cleaner, more maintainable, and highly performant code.

The functionality is centered around a categorized library of code snippets. Each entry provides an 'Old way'—typically requiring complex hacks or third-party JavaScript libraries—and a 'Modern' equivalent that utilizes native browser features available today. These comparisons cover a vast spectrum of web development tasks, from layout and animation to accessibility and form handling, ensuring that developers can easily find the right tool for their specific needs. The reference section provides detailed documentation on 737 CSS properties and 120 selectors, complete with syntax details and browser support data derived from industry-standard sources like Can I Use.

Some of the key features are:

• Side-by-Side Comparisons: Every snippet clearly visualizes the transition from legacy, complex code to modern, declarative CSS solutions.
• Browser Compatibility Mapping: Each feature is categorized by its 'Baseline' status, making it easy to know if a feature is ready for production use.
• Extensive Reference Library: A deep database covering hundreds of CSS properties, selectors, at-rules, and functions.
• No-JS Replacements: A strong focus on replacing JavaScript-dependent patterns with robust CSS-only alternatives for better performance and accessibility.
• Tutorials and Articles: In-depth guides that walk developers through building complex components like carousels and tooltips without external dependencies.

The project is designed for developers of all skill levels, from those learning the basics of layout to advanced engineers seeking to optimize their projects with the latest CSS specifications. Users can explore snippets by category, consult the comprehensive property and selector references, or read detailed tutorials that explain the 'why' behind these modern advancements. The site is actively maintained with a changelog and keeps track of ongoing web platform developments, such as the Interop 2026 focus areas.

Some common use cases include:

• Refactoring Legacy Code: Identifying areas in an existing codebase where modern native features can replace bloated or fragile hacks.
• Learning New Syntax: Quickly finding the native implementation for complex layouts like multi-column designs or vertical centering.
• Optimizing Performance: Reducing reliance on heavy JavaScript libraries by adopting native CSS features like scroll-driven animations and the Popover API.
• Improving Accessibility: Leveraging native elements like the <details> and <dialog> tags to ensure accessible, keyboard-navigable components without manual wiring.