Modern CSS

Choose native CSS features that fit the requested behavior and supported browsers. The user's explicit instructions take precedence over this skill's guidelines. Preserve the project's framework, preprocessor, tokens, and styling conventions unless changing them is part of the request.

Resolve the styling problem

Use the affected markup/styles, desired appearance or interaction, and browser targets as input. Infer targets from project configuration when available. If missing support information changes the implementation, ask for it or state a conservative fallback.

Bundled support tables are dated research snapshots, not a current compatibility guarantee. Check MDN compatibility data or Web Platform Status for the particular feature when support matters.

Need	Starting point
Rows and columns, or aligned nested tracks	Grid / Subgrid
One-dimensional arrangement	Flexbox
Layout based on a component's available space	Container queries
Cascading overrides or specificity conflict	Layers, scope, selector specificity
Themes and derived colors	Custom properties, color functions, color-scheme
Motion, popovers, or scroll effects	Feature-specific reference and fallback

Keep the result usable

• Preserve layout and interaction in supported browsers. Use progressive enhancement or feature detection where a feature is unavailable.
• Match cascade changes to the existing origin, importance, and layer ordering; adding a layer can change precedence.
• Respect reduced-motion preferences and preserve focus/keyboard behavior when changing interactive components.
• Use modern CSS as an option, not a mandate to remove JavaScript or rebuild working controls. Support and equivalent behavior determine whether a replacement fits.
• Scope resets and stylesheet reorganization to the task; a component edit does not require a global reset.

Deliver the requested style change or explanation and verify affected layout/states when implementing. State unverified browser limitations rather than treating an example as proof of support.

References

Load only the relevant area, using its contents to find specific features.

Task	Reference
Layers, scope, nesting, specificity	CASCADE.md
Grid, Flexbox, containers, intrinsic sizing	LAYOUT.md
Relational selectors, focus, pseudo-elements	SELECTORS.md
Color spaces, palettes, dark mode	COLOR.md
Custom properties, functions, design tokens	TOKENS.md
Transitions, keyframes, entry/exit, view transitions	ANIMATION.md
Scroll timelines, sticky states, carousels	SCROLL.md
Dialogs, popovers, anchors, selects, field sizing	COMPONENTS.md
Rendering performance, typography, writing modes	PERFORMANCE.md
Compact syntax or feature-detection lookup	CHEATSHEET.md