The Differing Perspectives On CSS In JS

CSS-in-JS was once hailed as the future of styling in React applications. Libraries like styled-components and Emotion promised to solve the global namespace problems of traditional CSS by bringing styling directly into the JavaScript component layer. Today, however, the frontend community has fractured into distinct camps, each with passionate opinions about the "right" way to style web applications.

This divergence isn't merely stylistic preference--it reflects fundamental trade-offs between developer experience, runtime performance, and long-term maintainability. As Next.js has evolved its recommendations, the industry has collectively shifted toward approaches that prioritize static extraction and zero runtime overhead.

Understanding these differing perspectives is essential for making informed decisions about your project's styling architecture. Whether you're building a new application from scratch or migrating an existing codebase, the choices you make around CSS methodology will impact every aspect of development--from initial velocity to long-term sustainability.

For teams working with complex styling requirements, understanding the fundamental rules of CSS provides a solid foundation for evaluating modern approaches.

The Rise And Promise Of CSS In JS

The story of CSS-in-JS begins with the growing pains of large-scale React applications. As teams built increasingly complex interfaces, traditional CSS began revealing its limitations: global namespace pollution, unpredictable selector collisions, and stylesheets that grew unwieldy as applications scaled. The React component model--where each piece of UI encapsulates its own logic and structure--seemed to demand a styling solution that could match that encapsulation.

CSS-in-JS libraries emerged to address these frustrations by treating styles as first-class JavaScript citizens. Rather than maintaining separate CSS files that could affect unexpected parts of the application, developers could co-locate styles with their components, use JavaScript's module system for organization, and leverage the full power of the language for dynamic styling based on props and state.

What CSS In JS Libraries Promised

The original promise of CSS-in-JS was compelling. Developers no longer needed to worry about class name collisions or maintain separate stylesheets that could affect unexpected parts of the application. Styles could be scoped to components automatically, and developers could use the full power of JavaScript to manipulate styles dynamically.

Key benefits that attracted early adopters:

• Automatic critical CSS extraction - Styles were generated only when needed
• Dead code elimination - Unused styles could be tree-shaken automatically
• JavaScript module system - Styles could be imported, exported, and shared like any other module
• Runtime theme variables - Theming became straightforward with dynamic theme context
• Server-side rendering support - Styles could be extracted rather than injected client during the build process-side

As The New Stack reported, these libraries initially seemed to solve the fundamental tension between CSS's flexibility and JavaScript's modularity. For a time, CSS-in-JS represented the cutting edge of frontend development--something that any modern React team should be using.

The Performance Problem

The initial enthusiasm for CSS-in-JS gave way to scrutiny as applications grew larger and performance became a more pressing concern. The fundamental trade-off that CSS-in-JS libraries made--trading build-time complexity for runtime flexibility--began to feel increasingly expensive as the web development community placed more emphasis on Core Web Vitals metrics.

Runtime Styling Versus Static Extraction

The fundamental issue with traditional CSS-in-JS libraries is that they generate styles at runtime. Every component render potentially involves JavaScript calculations to determine the final styles, adding overhead that pure CSS solutions avoid. This runtime cost becomes more pronounced as applications grow in complexity. The browser must wait for JavaScript to execute before knowing what styles to apply, which delays First Contentful Paint and Largest Contentful Paint metrics that directly impact user experience and SEO.

According to Next.js documentation, the framework has evolved its stance on CSS-in-JS libraries, now recommending approaches that enable static extraction--the ability to generate CSS at build time rather than runtime. Libraries that support this pattern can maintain the developer experience benefits of CSS-in-JS while avoiding the performance penalties of runtime styling.

The shift in industry sentiment reflects a broader recognition that the marginal developer experience benefits of runtime CSS-in-JS rarely justify the performance costs, especially when zero-runtime alternatives now exist that preserve much of the same ergonomics while producing pure CSS output.

The CSS Modules Approach

CSS Modules represent a return to pure CSS while solving the scoping problems that originally drove developers toward CSS-in-JS. With CSS Modules, you write standard CSS in files with a .module.css extension, and the build tool automatically generates unique class names at build time. This approach provides the best of both worlds: familiar CSS syntax with component-level scoping that eliminates the risk of global namespace collisions.

The developer experience with CSS Modules feels natural to those accustomed to traditional CSS while providing confidence that styles won't accidentally leak to other components. Since the generated CSS is static, there's no runtime overhead, and browser rendering is optimized since the styles are known at page load.

CSS Modules work seamlessly with modern build tools like webpack and Vite, and have excellent support in Next.js through built-in CSS processing. Teams with existing CSS expertise can adopt CSS Modules immediately without learning new APIs or abstractions.

For projects where the migration cost from traditional CSS is a concern, CSS Modules offer a gentle path forward that maintains the familiar workflow while adding the scoping guarantees that prevent stylesheet pollution as applications grow.

Understanding how CSS units like em and rem work alongside CSS Modules helps create truly scalable and maintainable styling systems.

The Tailwind CSS Phenomenon

Tailwind CSS represents a fundamentally different approach to styling that has dominated 2025. Rather than writing custom CSS for each component, developers apply small, single-purpose utility classes directly in their HTML. This approach eliminates the context switching between CSS files and component files, and the resulting styles are inherently scoped since each class does exactly one thing.

The configuration-driven nature of Tailwind allows teams to establish design systems programmatically. Colors, spacing, typography scales, and other design tokens are defined in a configuration file, ensuring consistency across the application while still providing the flexibility to create custom designs. This approach has proven particularly effective for teams building cohesive design systems.

When Tailwind Makes Sense

Tailwind excels in projects where design consistency is paramount and teams want to move quickly without constantly creating new CSS classes. The utility-first approach reduces the naming cognitive load--you don't need to think of creative class names when utilities already exist for every styling need.

However, Tailwind requires a shift in thinking. Some developers find the HTML markup becomes cluttered with numerous class names, potentially reducing readability. Projects with highly dynamic styling requirements or complex animations may need to supplement Tailwind with custom CSS or plugins. When comparing approaches, teams should consider whether the utility-first paradigm aligns with their existing workflows and team preferences.

For teams implementing CSS animations and visual effects, Tailwind's utility classes can be combined with custom CSS to achieve the best of both approaches.

Zero-Runtime CSS In JS Alternatives

The evolution of CSS-in-JS has produced a new category of libraries that extract styles at build time, eliminating runtime overhead entirely. Libraries like vanilla-extract, Linaria, and Astro's scoped styles allow developers to write type-safe, component-scoped styles that compile to static CSS files.

These zero-runtime solutions preserve many benefits of CSS-in-JS:

• Type safety - Full TypeScript integration for style properties
• Theming support - CSS custom properties generated at build time
• Modular styling - Component-scoped styles without runtime generation
• No runtime penalty - Output is indistinguishable from hand-written CSS

For teams committed to the CSS-in-JS mental model but unwilling to accept runtime costs, these libraries offer a compelling path forward. The developer experience closely resembles traditional CSS-in-JS--defining styles in JavaScript/TypeScript files alongside components--while producing pure CSS output that browsers can render immediately.

The trade-off is increased build time complexity and configuration requirements. Zero-runtime solutions require additional build steps to extract and process styles, which can slow down development feedback loops in larger projects. However, for teams that prioritize runtime performance and the developer experience of component-scoped styling, this trade-off is often worthwhile.

Choosing The Right Approach For Your Project

The "best" styling approach depends on your specific context. Each methodology has genuine strengths that make it the right choice for certain situations.

Decision Framework

Consider your performance budget carefully. While differences between approaches may be negligible for simple pages, complex applications with many components will feel the cumulative effect of runtime styling. Core Web Vitals metrics like First Contentful Paint and Cumulative Layout Shift can be directly impacted by styling approach choices.

The most successful teams evaluate these options against their specific constraints rather than following trends. A small team with strong CSS expertise might thrive with CSS Modules, while a large team building a design system might benefit more from Tailwind's consistency guarantees.

Best Practices Across All Approaches

Regardless of which styling approach you choose, certain principles improve maintainability and consistency across your application.

Design Token Architecture

Establishing design tokens--named variables for colors, spacing, typography, and other design values--ensures your application maintains visual coherence. Centralizing these tokens allows changes to propagate throughout the application consistently, whether you're using CSS custom properties, Tailwind's theme configuration, or JavaScript constants for zero-runtime solutions.

Component Library Considerations

Component libraries built on top of your styling approach abstract common patterns, reducing duplication and establishing patterns that team members recognize. Whether using Tailwind's component classes, CSS Modules compositions, or zero-runtime style files, consistent component architecture improves both development velocity and user experience.

Linting And Tooling

Invest in appropriate linting and formatting tooling regardless of your chosen approach. Stylelint, ESLint plugins, and Prettier configurations exist for all major styling methodologies. Consistent formatting prevents unnecessary diffs and helps maintain code quality as your codebase grows.

Server-Side Rendering Compatibility

Ensure your styling approach works correctly with server-side rendering to prevent hydration mismatches and flash of unstyled content. Modern frameworks like Next.js have specific recommendations for each approach, and following these guidelines helps deliver a smooth user experience.

Performance Optimization Strategies

Beyond choosing the right styling approach, specific techniques can help optimize styled applications for maximum performance.

Critical CSS Extraction

Modern build tools can extract critical CSS--styles required for above-the-fold content--into inline styles that load immediately, while deferring less critical styles. This approach balances the need for fast initial rendering with the maintainability benefits of component-scoped styles.

Bundle Size Analysis

Monitoring bundle size over time prevents styling libraries from growing unchecked. Use tools like webpack-bundle-analyzer to track the size of styling dependencies and establish budgets for CSS bundle size in your CI/CD pipeline. The shift away from traditional CSS-in-JS was largely driven by these bundle size concerns, so maintaining visibility into styling dependencies helps prevent regression.

Code Splitting Styles

For larger applications, consider splitting styles by route or component lazy loading. This ensures users only download the styles they need for the content they're viewing, reducing initial page load time and improving perceived performance.

Lazy Loading Components

Complex styled components that aren't immediately visible can be lazy-loaded using React's lazy and Suspense. This defers both the JavaScript and associated styles until they're needed, improving initial bundle size and Time to Interactive.

Conclusion

The CSS-in-JS debate continues because each approach genuinely solves different problems well. The industry has matured beyond treating any single methodology as universally correct. Today's best practice is matching your styling approach to your project's specific requirements, team capabilities, and performance goals.

For modern Next.js projects, the recommended path involves:

• CSS Modules for component-level styling with zero runtime overhead and familiar syntax
• Tailwind CSS for rapid UI development with design system integration and team consistency
• Zero-runtime CSS-in-JS solutions when type-safe styling with JavaScript semantics is essential

Each approach has earned its place in the ecosystem, and the thoughtful developer will choose based on context rather than ideology. Whether you're building a marketing site, a complex dashboard, or a design system, the right choice depends on your specific constraints and goals.

If you're evaluating styling approaches for a new project or considering migration from an existing solution, our web development team can help you assess the trade-offs and implement the approach that best fits your needs.

Sources

1. Next.js Official CSS-in-JS Guide - Framework recommendations and supported libraries
2. The New Stack: CSS-in-JS The Great Betrayal - Performance and developer experience perspective
3. Medium: Styling Strategies in Next.js 2025 - Comparative analysis of CSS approaches
4. Styled Components Fading Out in 2025 - Modern alternatives discussion
5. Superflex: CSS Modules vs Styled Components vs Tailwind - Comprehensive comparison