Write maintainable, performant CSS using modern methodologies including Tailwind CSS utility classes, CSS modules, CSS-in-JS, or design system tokens. Use this skill when styling components, creating layouts, implementing design systems, or working with CSS files (.css, .scss, .module.css), Tailwind configuration, styled-components, or CSS-in-JS solutions. Apply this skill when implementing utility-first patterns with Tailwind, using CSS custom properties for theming, creating responsive layouts with flexbox/grid, managing design tokens (colors, spacing, typography), or optimizing CSS for production with purging and tree-shaking. This skill ensures consistent styling methodology across the project, minimizes custom CSS when framework utilities exist, maintains design system coherence, and follows modern CSS best practices including container queries, CSS variables, and performance optimization.