CSS Does Not Scale by Default

CSS is globally scoped — every class name exists in a single global namespace. In a small project, this is manageable. In a large application with hundreds of components and multiple developers, global CSS becomes unmaintainable: naming collisions, specificity wars, dead CSS accumulation, and unpredictable side effects. At Nexis Limited, we use Tailwind CSS as our primary styling approach, supplemented by design tokens for consistency.

Methodology Comparison

Tailwind CSS

Utility-first CSS framework where styles are applied directly in HTML class attributes. No CSS files to maintain, no naming collisions, no dead CSS, and excellent tree-shaking. Our preferred approach for all projects.

Pros: Fast development, no naming decisions, automatic dead code elimination, consistent spacing/color system, excellent documentation.

Cons: Verbose class attributes, requires learning utility names, custom designs need configuration.

CSS Modules

Locally scoped CSS files that generate unique class names at build time. Each component has its own .module.css file with class names that are guaranteed unique. Built into Next.js and most modern frameworks.

Pros: Familiar CSS syntax, automatic scoping, no runtime overhead, works with any CSS features.

Cons: Requires managing CSS files alongside components, no design system built-in, harder to share styles.

CSS-in-JS (styled-components, Emotion)

Write CSS in JavaScript, co-located with component code. Styles are generated at runtime and scoped to the component. Dynamic styles based on props are natural.

Pros: True component scoping, dynamic styling, co-location with component code.

Cons: Runtime performance overhead, larger JavaScript bundles, SSR complexity, incompatible with React Server Components (major limitation in Next.js App Router).

BEM (Block Element Modifier)

Naming convention (.block__element--modifier) that prevents naming collisions through disciplined naming. No tooling required — just convention.

Pros: No build tools needed, predictable naming, works everywhere.

Cons: Relies on team discipline, verbose class names, no enforcement mechanism, does not prevent specificity issues.

Design Tokens

Design tokens are the single source of truth for design decisions — colors, spacing, typography, shadows, and border radii. Define tokens as CSS custom properties or Tailwind config values and reference them throughout the application. Never use hardcoded values.

  • Colors: Define a semantic color palette (primary, secondary, success, error, text-primary, text-secondary, background).
  • Spacing: Use a consistent spacing scale (4px, 8px, 12px, 16px, 24px, 32px, 48px, 64px).
  • Typography: Define font family, size scale, weight scale, and line height tokens.
  • Shadows: Define a shadow scale (sm, md, lg, xl) for consistent elevation.

Organizing Styles in Large Projects

Component-Level Organization

Co-locate styles with their components. Each component directory should contain the component code and its styles. This makes components portable and eliminates searching for style definitions across separate directories.

Global Styles

Keep global styles minimal — only CSS resets, font imports, CSS custom property definitions, and base element styles (body, headings, links) should be global. Everything else should be component-scoped.

Removing Dead CSS

Over time, CSS accumulates unused styles. Use PurgeCSS (built into Tailwind) to remove unused styles from production builds. For CSS Modules, unused exports generate warnings. Track CSS bundle size over time to catch growth.

Best Practices

  • Pick one methodology and use it consistently across the entire project.
  • Define design tokens before writing component styles.
  • Avoid !important — if you need it, there is a specificity issue to fix.
  • Use CSS logical properties for internationalization readiness.
  • Test styles across browsers and screen sizes in CI with visual regression tools.
  • Document your CSS architecture in the project README or contribution guide.

Conclusion

CSS architecture matters at scale. Choose a methodology that provides scoping (Tailwind, CSS Modules, CSS-in-JS) rather than relying on naming conventions alone. Define design tokens for consistency. Keep global styles minimal. The investment in CSS architecture prevents the creeping chaos that makes large applications hard to maintain.

Building a design system? Our frontend team creates scalable CSS architectures.