| name | design-system |
| description | Mechanical implementation invariants for frontend design: token architecture, typography hierarchy, loading order, FOUT prevention, chrome stability, motion timing, color semantics. Use with design wh |
Design system
When to Use
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).
- 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-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
<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 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: 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 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> scen
