Design system
Mechanical implementation invariants for frontend design: token architecture, typography hierarchy, loading order, FOUT prevention, chrome stability, motion timing, color semantics. Use with design when building components, pages, or design systems. (Aesthetic direction lives in design-thinking; anti-trend/anti-slop in design-spatial.)From its SKILL.md
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Design system
Apply with design when implementing UI: components, pages, or design systems. Every color, type, and motion choice should trace back to these rules.
Token architecture
All colors map to a small set of primitives. No random hex values.
- Foreground: Text hierarchy (primary, secondary, muted).
- Background: Surface elevation (base, raised, overlay).
- Border: Separation hierarchy (subtle, default, emphasis).
- Brand: Identity and primary accent.
- Semantic: Destructive, warning, success (and optional info).
Use tokens in code (CSS variables, theme objects); never hardcode hex for UI.
Typography
- Hierarchy: Headlines — heavier weight, tighter letter-spacing for presence. Body — comfortable weight for readability. Labels/UI — medium weight, works at smaller sizes. Data — monospace,
tabular-numsfor alignment. - Combine size, weight, and letter-spacing so hierarchy is clear at a glance. If you squint and can't tell headline from body, hierarchy is too weak.
- Fonts: pair a display font with a body font; keep hierarchy legible at a glance. Which fonts is direction, not mechanics — pick from the domain and push off your first/default instinct (the mean); see design-spatial §2.
- Data (functional only): real aligned numbers, IDs, timestamps in monospace with
tabular-nums— mono earns its place when values line up in a column. Do NOT sprinkle mono on decorative eyebrow/metadata microtext ("35MM · DEVELOP · SCAN", fake spec captions) for a "technical" look — that's the current trend-slop, not data. See design-spatial §2.
Loading order — first seen, first loaded
The first viewport must paint complete and correct, fast. Order every resource by whether the user sees it first; the rest waits.
- Prioritize only the above-the-fold set (hero text, hero image/video, brand mark). Preloading everything is the same as preloading nothing — the true criticals lose the bandwidth race. Pick the few things in the first screenful and prioritize those.
- Fonts: self-host WOFF2. Convert OTF/TTF → WOFF2 (Brotli; ~half the bytes, identical glyphs) and
<link rel="preload" as="font" type="font/woff2" crossorigin>the weights used in the first viewport. Never a render-blocking third-party font stylesheet — a Google Fonts<link>adds a CSS round-trip plus extra DNS/TLS before the font even starts downloading; self-host instead. - LCP image/video:
fetchpriority="high"on the hero image (or the video poster);<link rel="preload" as="image">it when it's CSS-referenced (the parser can't see CSSurl()s early). The hero box must never be empty — ship a poster/low-res placeholder so there's no blank frame. - Below the fold:
loading="lazy" decoding="async"on images;preload="none"(or"metadata") on video;defernon-critical JS. Always reserve space (aspect-ratio, orwidth+height) so deferred media can't shift layout (CLS). - Keep the render-blocking head minimal: inline critical CSS, defer the rest.
Never let fonts pop in (no FOUT) — ever
font-display: swap is the pop — it paints a fallback face, then swaps to the webfont and reflows. Do not use it for any text the user watches load (titles, wordmarks, hero copy). The rule is absolute: title/display text must never flash a fallback or reflow.
- Gate visibility on the real font. Synchronously in
<head>, add afonts-pendingclass to<html>that holds the display-font text atopacity: 0. Ondocument.fonts.ready— kick it withdocument.fonts.load('<weight> 1em "Family"')for each critical face — swap tofonts-readyand fade the text in (~0.5s). Always include a safety timeout (~2.5s) that reveals regardless, so a font failure can never leave text permanently hidden. - Pair this with preload + WOFF2 (above) so the hidden window is a few hundred ms, not seconds — the fade reads as intentional, not as a stall.
- For body text where a sub-perceptual swap is tolerable, at minimum kill the reflow: define a fallback
@font-face(orfont-familyfallback) tuned withsize-adjust/ascent-override/descent-overrideso the fallback occupies the same metrics as the webfont and the swap shifts nothing.
Worked example — an AR product-research page: a head script toggles fonts-pending → fonts-ready (titles fade in on fonts.ready, 2.5s fallback), preloads the four above-the-fold WOFF2 weights, and self-hosts the brand face so there's no Google round-trip.
Slow-loading content — never show the ugly intermediate state
Anything that could take a noticeable moment to be ready — fonts (above), large images, video, <canvas> scenes, Three.js / WebGL, lazy-loaded React islands, anything that fetches over the network or runs heavy main-thread setup — must either arrive fast or load gracefully. The default browser behavior (blank box → partial paint → reflow → final state) is the ugly intermediate state. Catch it.
Two levers; use both:
- Arrive faster. Compress (WOFF2 for fonts, Draco for glTF, WebP/AVIF for images, h264/h265 for video with
preload="metadata"). Preload the few assets the first viewport actually needs (<link rel="preload">). Lazy-load below-the-fold so the LCP set isn't competing. Reserve the box (aspect-ratio,width+height) so deferred content can't trigger CLS. - Load gracefully. Hide the in-flight state behind a styled placeholder, then fade the real thing in. Skeleton boxes, low-res blurred posters, a single ASCII glyph, even just the container's bg color — anything coherent with the design beats the default partial-paint.
What "ugly" looks like, concretely, and the fix:
| Symptom | Fix |
|---|---|
Annotation labels stack at translate(0,0) (top-left of container) until JS positions them | Start labels at opacity: 0 with a transition: opacity ~0.35s; first projection sets inline opacity → CSS fades them up. |
| Canvas/WebGL paints empty/black for a frame on first render | Show a placeholder (CSS art, low-res poster image, or paper/skeleton fill) in the same box; remove it once the first real frame has rendered. |
| Lazy image fetches and snaps in with a layout-jump | aspect-ratio + <link rel="preload"> (above-the-fold) or loading="lazy" decoding="async" (below); fade from opacity:0 on the load event for the first paint. |
| Video poster pops to first frame on play | poster matches a still you control; once playing event fires, you've already had a clean handoff. |
| 3D model "appears" mid-screen with no transition | Keep the canvas visible but at opacity: 0; toggle a .viewer-ready class (or set inline opacity) inside the GLTFLoader success callback, after the first tick(). |
| Lazy React island flashes a fallback that looks worse than no UI | Replace Suspense fallback with a skeleton that traces the final layout, not a spinner. |
Rule of thumb: if a user could screenshot the page mid-load and you'd be embarrassed, you owe it a graceful state. The placeholder doesn't have to be fancy — it has to be intentional, sized correctly, and in the design language of what's coming.
Chrome stays still — status text never resizes layout
Persistent chrome (headers, nav, toolbars, search bars, status regions) must hold a constant height no matter what text lands in it. Transient status / loading / explanatory copy — "loading model…", "N matching · M indexed", empty-state hints — must not wrap to a second line and shove adjacent controls down. A status region that grows and shrinks as its message changes is a layout-jank bug, not dynamic content.
- Constrain to one line:
white-space: nowrap; overflow: hidden; text-overflow: ellipsisso the longest message truncates instead of wrapping. - Reserve the space up front: give the container a fixed
height(ormin-height) sized for the message, so the shortest and longest states — and the empty state — occupy the same footprint.
Only the content area should move while chrome stays fixed; layout shift from transient text reads as broken polish. (Concrete failure this prevents: in a search app, a model-loading message wrapping to two lines and pushing the search bar downward.)
Motion
- Keep timing consistent and purposeful; one well-orchestrated moment (staggered page load with
animation-delay) beats scattered micro-interactions. Prefer CSS-only for HTML; Motion library for React. (Honorprefers-reduced-motionfor public/multi-user projects.) - Defaults for restrained/professional UIs (a starting point, not law): micro-interactions ~150ms, larger transitions 200–250ms, ease-out. A playful/toy-like tone (design-thinking) may want spring/bounce and longer beats — match motion feel to the chosen direction rather than defaulting to these numbers.
- Choreography — for anything beyond a single micro-interaction (route/page transitions, list reorder, reveals, shared elements), load references/motion-choreography.md: when a transition earns its keep (it must communicate something or get cut), which kinds to implement and in what order, style by navigation type (directional slide only for hierarchical/ordered — a slide between peers lies about depth; laterals fade), a duration table, and craft (compositor-only props, motion-blur on morphs, never raster-scale text, persistent-chrome isolation). Framework-agnostic.
Scroll-driven narrative (scrollytelling)
For explanatory / editorial / data-walkthrough content, prefer scroll-driven graphics over click-interactive widgets. A reader scrolls by default; making them hunt for and click a toggle to advance an explanation adds friction and gets skipped. Use the NYT/Pudding pattern: pin one graphic (position: sticky) while short text "steps" scroll past it, and let each step drive the graphic's state.
- Mechanics: one
IntersectionObserverwithrootMargin: '-48% 0px -48% 0px'(threshold 0) so a step goes "active" exactly as it crosses the viewport mid-line; the active index re-renders the pinned graphic. ~30 lines — this is scrollama minus the dependency; don't add a scroll library. - Layout: two columns — steps scroll in one, the graphic
sticky top-0 h-screenin the other; stack on mobile with the graphic sticky on top. Give each step ~85vh so exactly one is centered at a time; dim the inactive step cards (opacity:.3) so the live one reads. - Graphic is a pure function of the active step (
graphic(active)), holding no click state of its own — so it also screenshots/exports deterministically and degrades to a static figure. Animate between states (color / width / opacity, 300–700ms) so scrolling feels continuous, not steppy. - When NOT to: dashboards, tools, forms — anything the user operates rather than reads — stay interactive. Scrollytelling is for narration, where you own the order. (Public/multi-user builds: honor
prefers-reduced-motionper the Motion note above; keep the state changes but drop the tweens.)
Spatial composition & layout
Grid systems, the 8-point spacing scale, visual-weight balance, alignment, and the render-then-critique loop live in design-spatial (../design-spatial/SKILL.md) — the mechanical counterpart to this file's tokens/type/color. Load it whenever composing pages, dashboards, or components. (Direction nugget that belongs here: match composition ambition to the vision — maximalist earns elaborate/layered code; minimal/refined demands restraint and precise spacing.)
Nested radii (only when one rounded element sits inside another)
Not a push to round things — this governs the case where a rounded element is nested in another (a button in a card, an inset panel in a container). When nested:
- Child radius ≤ parent radius, never larger (a child corner rounder than its parent looks like it's bulging out).
- Concentric is the ideal:
child_radius = parent_radius − gap(the padding between them), so the two curves run parallel and the inner corner echoes the outer. Flat/unrounded children in a rounded parent are fine; what reads as broken is mismatched, non-concentric curves.
Color
- Palette from domain: colors should feel like they came from the product's world, not applied on top.
- Beyond temperature: quiet vs loud, dense vs spacious, serious vs playful, geometric vs organic — not just warm/cool.
- Color carries meaning: gray builds structure; color communicates status, action, emphasis, identity. Unmotivated color is noise. (Restraint — one accent, not five — is a direction principle; see design-thinking → reserve impact for punctuation.)
- Contrast — APCA for decisions, WCAG for the gate. For perceptual contrast judgments (is this text comfortably readable on this surface?) prefer APCA (apcacontrast.com) — it models lightness perception far better than the WCAG 2 ratio, which mis-rates light-on-dark and mid-tones. Keep WCAG 2 (4.5 / 3:1) as the compliance floor — it's what
design-spatial'slayout-audit.jsgates on and what accessibility standards require. Use APCA to design, WCAG to certify. - Interactive states gain contrast.
:hover,:active,:focusmust read as more prominent than rest — more contrast, not less. A hover that lowers contrast (e.g. lightens text toward the bg) reads as disabled.
Avoiding the generic/trend look (Inter, purple-on-white, the same dark-glass card) and varying across generations is design-spatial §2 — not restated here.
Backgrounds & detail
Atmosphere over flat fills — but matched to the chosen aesthetic, not a default. The reflexive gradient-mesh / noise / grain "premium" treatment is itself the designer-trend mean (design-spatial §2); reach for it only when the direction genuinely calls for it, never as decoration for its own sake.
What ships with it: 1 file
6.4 KB alongside SKILL.md
references/
- motion-choreography.md6.4 KB