CSS-AI CSS help and generator
AI-powered CSS expert for building, debugging, and optimizing styles.
Your personal highly sophisticated CSS copilot, with a focus on efficient, beautiful, scalable and high-quality production code
⚙️ Add hover animations to this HTML
🖌️ Write a beautiful CSS for my HTML code
⭐️ Create an amazing animation with CSS
💡 Teach me a useful skill or trick in CSS
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CSS, in practice
CSS (Cascading Style Sheets) is the language that turns semantic HTML into a designed, responsive interface. Its purpose is to control presentation—layout, spacing, color, typography, motion, and states—separately from content and behavior. The “cascade” and “specificity” rules decide which styles win, while inheritance reduces repetition. Modern CSS gives you powerful primitives (Grid, Flexbox, custom properties, container queries, cascade layers, media queries) to build design systems that scale from a single landing page to multi-app platforms. Example — same HTML, two brands: - A product card’s HTML stays identical. Brand A and Brand B swap tokens like --brand-500, --bg, --radius, instantly re-skinning the UI without touching the markup or JavaScript. Scenario — progressive enhancement: - Start with readable HTML. Add layout with Grid/Flex. Layer on motion and advanced selectors (e.g., :has()) where supported. Users on older browsers still get a usable page; modern browsers get the polished experience.
What CSS actually does for you
Layout & responsive composition
Example
Build adaptive grids and components that rearrCSS introduction and functionsange as space changes using Grid, Flexbox, and container queries. ```css .product-grid { display: grid; grid-template-columns: repeat(auto-fill, minmax(16rem, 1fr)); gap: 1rem; } .card { display: grid; grid-template: 'media' auto 'body' 1fr / 1fr; container-type: inline-size; /* enable container queries */ border: 1px solid hsl(210 10% 80%); border-radius: .75rem; padding: 1rem; } @container (min-width: 28rem) { .card { grid-template: 'media body' auto / 12rem 1fr; column-gap: 1rem; } .card .media { grid-area: media; } .card .body { grid-area: body; } } @media (min-width: 80rem) { .product-grid { gap: 1.25rem; } } ```
Scenario
E-commerce listing: on phones, cards stack with image above text; in wider containers (e.g., a sidebar or a 2-column layout), the card switches to a two-column internal layout without a global breakpoint, thanks to container queries. Devs avoid complex JS resize listeners and keep the component portable.
Visual styling, tokens & theming
Example
Use custom properties (CSS variables) as design tokens, swap themes via attributes, and control precedence with cascade layers. ```css @layer reset, tokens, base, components, utilities; @layer tokens { :root { --bg: #ffffff; --text: #0a0a0a; --brand-500: hsl(250 80% 60%); --radius: .75rem; --space-2: .5rem; --space-4: 1rem; } [data-theme='dark'] { --bg: #0b0f14; --text: #e6edf3; --brand-500: hsl(250 80% 65%); } @media (prefers-color-scheme: dark) { :root:not([data-theme]) { --bg:#0b0f14; --text:#e6edf3; } } } @layer base { html, body { background: var(--bg); color: var(--text); } } @layer components { .btn-primary { background: var(--brand-500); border-radius: var(--radius); padding: var(--space-2) var(--space-4); color: white; } } ```
Scenario
SaaS app with white-labeling: ship one codebase to multiple clients. Each client gets a tiny theme file overriding tokens (colors, corner radius, spacing scale). Dark mode is automatic via prefers-color-scheme unless a user explicitly selects a theme. Cascade layers keep resets/tokens/base from accidentally overriding component intent.
State, interaction & motion (without JS)
Example
Style interactive states and micro-interactions with selectors (:hover, :focus-visible, :has(), :disabled, :invalid), transitions, and keyframes—respecting reduced motion. ```css /* Accessible focus & micro-interactions */ .button { --e: .2s ease; background: var(--brand-500); color: #fff; border-radius: .6rem; padding: .6rem 1rem; transition: transform .1s var(--e), background var(--e), box-shadow var(--e); } .button:hover { box-shadow: 0 6px 16px hsl(250 60% 40% / .25); } .button:active { transform: translateY(1px); } .button:focus-visible { outline: 3px solid hsl(45 100% 50% / .6); outline-offset: 3px; } /* Form validation & helper text */ input:invalid { border-color: hsl(0 70% 50%); } input:invalid + .hint { color: hsl(0 70% 45%); } /* CSS-only disclosure using :has() */ .details:has(.toggle:checked) .panel { max-height: 40rem; } .panel { max-height: 0; overflow: clip; transition: max-height .25s ease; } /* Respect user preferences */ @media (prefers-reduced-motion: reduce) { * { transition-duration: 0s !important; animation-duration: .01ms !important; } } ```
Scenario
Marketing site: buttons feel tactile; keyboard users get clear focus rings. A FAQ accordion opens via a checkbox + :has()—no JS. Forms surface errors through :invalid instantly. Users who prefer reduced motion see instant state changes without blurred animations, improving accessibility and comfort.
Who benefits most from CSS
Front-end developers & web engineers
They translate designs into resilient UI. CSS gives them precise control over layout (Grid/Flex), robust responsiveness (container queries), and maintainability (custom properties, cascade layers). Engineers building design systems rely on tokens and layering to scale across apps, while accessibility features (focus-visible, reduced-motion, high-contrast friendly color choices) help them meet compliance and user needs. For performance, modern CSS (content-visibility, contain, logical properties) reduces reflow and improves rendering without extra JS.
Product designers & design-system teams
They define visual language and interaction patterns. CSS lets them codify spacing, typography, color, and motion as tokens so Figma specs map 1:1 to code. Designers can prototype states and micro-interactions with pure CSS, then ship the same styles into production. Design-system teams benefit from themeability (brand skins, dark mode), consistent component APIs (class contracts, utilities), and predictable overrides via layers—enabling faster iteration and fewer regressions across large product suites.
How to Use CSS in 5 Steps
Get Access
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Setup & Include
Create an HTML file and link a stylesheet: <link rel="stylesheet" href="styles.css">. Prefer external CSS for caching and maintainability. Know precedence: inline > internal > external; later rules win within the same origin. Prereqs: a text editor, a modern browser, and basic HTML.
Author Solid Styles
Use reset/normalize and box-sizing:border-box; define tokens with CSS variables (:root { --space-2: .5rem; --brand: #4f46e5; }). Write predictable selectors (class-based, BEM), understand cascade/specificity, and avoid !important. Use modern units (rem, ch, lh), logical properties (margin-inline), and system fonts or performant font loading.
Layout & Responsive
Use Flexbox for 1D alignment and Grid for 2D layout (minmax, auto-fit). Embrace fluid sizing (clamp(), vw) and media/container queries. Respect user prefs (prefers-reduced-motion), ensure accessible color contrast, and test with real content ranges.
Debug, Test,How to use CSS Optimize
Use browser DevTools (hover rules, toggle states), @supports for fallbacks, and cross-browser checks. Ship critical CSS inline, defer the rest; minify and purge unused styles. Audit performance (style recalcs/paint), accessibility (focus states), and maintain versioned design tokens.
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Five In-Depth CSS Q&A
How do you help resolve CSS specificity conflicts cleanly?
I calculate specificity (inline:1,0,0,0; ID:0,1,0,0; class/attr/pseudo-class:0,0,1,0; element/pseudo-element:0,0,0,1), surface the winning rule, and suggest fixes: simplify selectors, reorder within cascade layers (@layer base, components, utilities), replace !important with better structure, and leverage :where() to add grouping without extra specificity. I also recommend BEM naming and isolating third-party CSS inside its own layer.
Can you generate a responsive layout with modern CSS and safe fallbacks?
Yes. Example: ```css /* tokens */:root{--gap:clamp(.75rem,2vw,1.25rem)} .container{container-type:inline-size;} .grid{display:grid;gap:var(--gap); grid-template-columns:repeat(auto-fit,minmax(clamp(12rem,33vw,20rem),1fr));} @container (min-width:40rem){.card{display:flex;gap:var(--gap);}} @supports not (container-type:inline-size){ /* fallback */ .grid{grid-template-columns:repeat(auto-fit,minmax(16rem,1fr));} } ``` I’ll tailor tokens, breakpoints, and fallbacks to your content.
What’s your approach to cross-browser compatibility?
Start with progressive enhancement: use @supports for advanced features, provide simple fallbacks, and keep layout resilient (no absolute breakpoints). Prefer standards over vendor quirks, use PostCSS/Autoprefixer in the build, test on evergreen browsers and at least one legacy baseline. Avoid deprecated features (@import in CSS), and rely on logical properties to reduce locale/layout issues.
How do you structure and theme design tokens with CSS variables?
Define semantic tokens in :root (e.g., --color-bg, --space-3), map component vars to them, and switch themes with an attribute: [data-theme="dark"] { --color-bg:#0b0b0f; --color-fg:#e6e6ef; }. Scope component overrides on the smallest container possible. For runtime theming, toggle data-theme on <html> and respect prefers-color-scheme for initial load.
What are key CSS performance practices you recommend?
Inline critical CSS for above-the-fold, async/defer non-critical via media=print+onload or preload+media. Minify and tree-shake unused rules; avoid heavy universal/descendant selectors that trigger deep matching. Use content-visibility:auto and contain for large sections; animate transform/opacity only; be cautious with will-change. Preload fonts, use font-display:swap, and subset character sets.