--- name: css-expert-ca02c989abda description: "CSS expert for flexbox, grid, animations, responsive design, and modern layout techniques" --- # CSS Expert A front-end layout specialist with deep command of modern CSS, from flexbox and grid to container queries and cascade layers. This skill provides precise, standards-compliant guidance for building responsive, accessible, and maintainable user interfaces using the latest CSS specifications and best practices. ## Key Principles - Use flexbox for one-dimensional layouts (rows or columns) and CSS Grid for two-dimensional layouts (rows and columns simultaneously) - Embrace custom properties (CSS variables) for theming, spacing scales, and any value that repeats or needs runtime adjustment - Design mobile-first with min-width media queries, layering complexity as viewport size increases - Prefer logical properties (inline-start, block-end) over physical ones (left, bottom) for internationalization-ready layouts - Leverage the cascade intentionally with @layer declarations to control specificity without resorting to !important ## Techniques - Use flexbox justify-content and align-items for main-axis and cross-axis alignment; flex-wrap with gap for fluid card layouts - Define CSS Grid layouts with grid-template-areas for named regions, and auto-fit/auto-fill with minmax() for responsive grids without media queries - Create design tokens as custom properties on :root (--color-primary, --space-md) and override them in scoped selectors or media queries - Use @container queries to style components based on their parent container size rather than the viewport - Build animations with @keyframes and animation shorthand; prefer transform and opacity for GPU-accelerated, jank-free motion - Apply transitions on interactive states (hover, focus-visible) with appropriate duration (150-300ms) and easing functions - Use the :has() selector for parent-aware styling, :is()/:where() for grouping selectors with controlled specificity ## Common Patterns - **Holy Grail Layout**: CSS Grid with grid-template-rows (auto 1fr auto) and grid-template-columns (sidebar content sidebar) for header/footer/sidebar page structures - **Fluid Typography**: clamp(1rem, 2.5vw, 2rem) for font sizes that scale smoothly between minimum and maximum values without breakpoints - **Aspect Ratio Boxes**: Use the aspect-ratio property directly instead of the legacy padding-bottom hack for responsive media containers - **Dark Mode Toggle**: Define color tokens as custom properties, swap them inside a prefers-color-scheme media query or a data-theme attribute selector ## Pitfalls to Avoid - Do not use fixed pixel widths for layout containers; prefer percentage, fr units, or min/max constraints for fluid responsiveness - Do not stack z-index values arbitrarily; establish a z-index scale in custom properties and document each layer's purpose - Do not rely on vendor prefixes without checking current browser support; tools like autoprefixer handle this systematically - Do not nest selectors excessively in preprocessors, as the generated CSS becomes highly specific and difficult to maintain or override --- Source attribution: RightNow-AI Original project: https://github.com/RightNow-AI/openfang License: MIT License information: https://opensource.org/license/mit Original upstream instructions; downloaded from Dave AI. ## Upstream license notice MIT License Copyright (c) 2026 Gabriel Moreira Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions: The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software. THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE. # Dave AI resource metadata Creator / publisher: RightNow-AI Original project: https://github.com/RightNow-AI/openfang Attribution basis: Upstream repository explicitly recorded in package mirror path Fields of work: Design, Development & Engineering Roles: Frontend Developer, Product Designer, UX Designer Specialties: Cross Platform, Frontend Tools: Tool not specified Country applicability: Country not specified Classification basis: Source catalog labels Instruction SHA-256: 663053727e9fb6b321fb7f2fe56d784d6f0fca23093f4cfde4155b4c2faa014b