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...
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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...
Use this skill when you need 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...
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).
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-nums for 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 the weights used in the first viewport. Never a render-blocking third-party font stylesheet — a Google Fonts 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 CSS url()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; defer non-critical JS. Always reserve space (aspect-ratio, or width+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: swapis 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 a fonts-pending class to <html> that holds the display-font text at opacity: 0. On document.fonts.ready — kick it with document.fonts.load('<weight> 1em "Family"') for each critical face — swap to fonts-ready and 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 (or font-family fallback) tuned with size-adjust / ascent-override / descent-override so 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: ellipsis so the longest message truncates instead of wrapping.
Reserve the space up front: give the container a fixed height (or min-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. (Honor prefers-reduced-motion for 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 IntersectionObserver with rootMargin: '-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-screen in 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-motion per 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's layout-audit.js gates on and what accessibility standards require. Use APCA to design, WCAG to certify.
Interactive states gain contrast.:hover, :active, :focus must 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.
Limitations
Use this skill only when the task clearly matches its upstream source and local project context.
Verify commands, generated code, dependencies, credentials, and external service behavior before applying changes.
Do not treat examples as a substitute for environment-specific tests, security review, or user approval for destructive or costly actions.
