Interface polish

Interface Polish

The last 10% that separates "works" from "feels great". Apply these rules to an interface whose layout, palette, and structure are already decided. Do not change the design direction — refine its execution.

Work through the sections as a checklist against the actual code. Fix what's missing; leave what's already right.

1. Interactive states

Every interactive element needs four distinct states: rest, hover, active, focus-visible. Missing states are the #1 "feels unfinished" signal.

.button {
  transition: background-color 150ms ease, box-shadow 150ms ease, transform 100ms ease;
}
.button:hover  { background-color: var(--accent-hover); }
.button:active { transform: scale(0.98); transition-duration: 50ms; } /* press responds FASTER than hover */
.button:focus-visible {
  outline: 2px solid var(--accent);
  outline-offset: 2px;   /* never outline: none without a replacement */
}

Rules:

• Hover changes must be subtle but unmistakable: one step of background shift, or 1–2px lift with shadow deepening — not both plus a color change.
• :active should feel physically pressed: scale 0.97–0.98 or translateY(1px), with a shorter duration than hover.
• Use :focus-visible, not :focus, so mouse clicks don't paint rings but keyboards do.
• Rows/list items: hover = background-color shift only; don't move them.
• Disabled: reduce opacity to ~0.5 AND remove hover effects (pointer-events: none or explicit rules).
• Touch: hover states must not be load-bearing; anything revealed on hover needs a touch/focus path too.

2. Transition timing and easing

• Durations: 100–150ms hover/press · 200ms dropdowns, tooltips · 250–300ms modals, drawers, layout shifts · 400–600ms only for page-level or decorative reveals. When unsure, subtract 50ms — slow transitions read as lag.
• Never transition: all. List properties explicitly; all causes accidental animation of layout properties and jank.
• Easing: ease-out for things appearing/responding to the user (start fast, settle). ease-in or ease-in-out for things leaving. cubic-bezier(0.16, 1, 0.3, 1) (expo-out) makes entrances feel expensive. Bounce/overshoot only if the design system is playful — and subtle (≤8% past target).
• Exit faster than enter: a modal opening at 250ms should close in ~180ms. Users wait for what appears; they've already dismissed what's leaving.
• Animate only compositor-friendly properties where possible: transform, opacity. Animating width/height/top/left/margin causes layout jank; if unavoidable, keep the element small or use transform tricks. Never animate box-shadow directly on large surfaces — crossfade a pseudo-element's opacity instead:

.card::after {
  content: ""; position: absolute; inset: 0; border-radius: inherit;
  box-shadow: var(--shadow-lg); opacity: 0; transition: opacity 200ms ease;
  pointer-events: none;
}
.card:hover::after { opacity: 1; }

3. Enter/exit animations

Elements should arrive from somewhere, not pop into existence.

• Pattern: fade + small movement. Opacity 0→1 plus translateY(8–12px)→0, or scale(0.96–0.98)→1 for popovers/modals. Movement over ~16px looks theatrical.
• Origin matters: dropdowns scale/slide from the trigger (transform-origin: top left or as appropriate), toasts slide from the edge they live on, modals scale from center.
• Exit animations require keeping the node until the animation ends. In CSS-only setups, prefer @starting-style + transition-behavior: allow-discrete (modern) or toggle a class and remove on transitionend. In React, use a presence utility or a two-step state (closing → closed).

dialog {
  opacity: 1; transform: scale(1);
  transition: opacity 200ms ease-out, transform 200ms cubic-bezier(0.16, 1, 0.3, 1),
              overlay 200ms allow-discrete, display 200ms allow-discrete;
}
@starting-style { dialog[open] { opacity: 0; transform: scale(0.97); } }
dialog:not([open]) { opacity: 0; transform: scale(0.98); }

• Height-into-view (accordions): animate grid-template-rows: 0fr → 1fr on a grid wrapper with min-height: 0 on the child — smooth without measuring heights.

4. Stagger

Lists that animate in as one block feel cheap; a small cascade feels orchestrated.

• Delay step: 30–60ms between items. Total cascade should finish under ~600ms — cap the delay after 8–10 items (min(index, 8) * 40ms).
• Stagger only on first entrance (page load, list appearing) — not on every re-render or filter change.

.list > * { animation: item-in 350ms cubic-bezier(0.16, 1, 0.3, 1) backwards; }
.list > :nth-child(1) { animation-delay: 0ms; }
.list > :nth-child(2) { animation-delay: 40ms; }
/* or dynamically: */

document.querySelectorAll(".list > *").forEach((el, i) => {
  el.style.animationDelay = `${Math.min(i, 8) * 40}ms`;
});

@keyframes item-in { from { opacity: 0; transform: translateY(10px); } }

animation-fill-mode: backwards prevents the pre-delay flash of the final state.

5. Shadows and elevation

• Single-layer shadows look flat. Layer a tight contact shadow with a soft ambient one:

--shadow-md: 0 1px 2px rgba(16, 24, 40, 0.06),   /* contact: small blur, small offset */
             0 8px 24px rgba(16, 24, 40, 0.10);  /* ambient: large blur, large offset */

• Shadow color: tint toward the background/brand hue instead of pure black — rgba(16,24,40,…) on cool UIs, warm equivalents on warm UIs. Pure black shadows look dirty on colored backgrounds.
• Y-offset grows with elevation; blur ≈ 2–3× offset; opacity DROPS as blur grows.
• Border vs shadow: static containers on a page → 1px border (or background shift), no shadow or a whisper (--shadow-xs). Floating ephemerals (menus, popovers, modals, drag previews) → shadow, plus a hairline border so edges survive on white-on-white. Shadow communicates "above the page"; if it doesn't float, it shouldn't cast much.
• Dark mode: shadows nearly disappear against dark backgrounds — convey elevation with lighter surface colors and borders instead; keep only a faint shadow for grounding.
• Inset highlight for a crisp premium edge on raised elements: box-shadow: inset 0 1px 0 rgba(255,255,255,0.08) (dark UIs) as an extra layer.

6. Border-radius nesting

Concentric corners: inner radius = outer radius − padding. A 16px-radius card with 8px padding needs 8px-radius children; giving them 16px too makes corners visibly clash.

.card  { border-radius: 16px; padding: 8px; }
.card > .thumb { border-radius: calc(16px - 8px); } /* = 8px */

• If the math gives ≤2px, use a small consistent value (2–4px) rather than 0 next to a large outer radius.
• Never mix radius scales on siblings (a 4px button beside a 12px button).
• Pills inside rounded containers are exempt (radius 999px reads as its own shape).
• Elements clipped at a rounded parent's edge need overflow: hidden on the parent or matching radius on the child, or corners will poke out.

7. Optical alignment

Mathematical centering is often visually wrong; trust the eye and nudge.

• Play/triangle icons in circles: shift right ~1–2px (visual mass sits left of the bounding box).
• Icons beside text: align to cap-height/x-height feel, not baseline math — usually translateY(-0.5px – 1px) or flexbox align-items: center plus a nudge.
• Text in buttons: many fonts render slightly low; padding-bottom: 1px less than top, or line-height tuning, makes labels look centered.
• Large display text: the bounding box includes side bearings; pull the first line left with margin-left: -0.05em to flush-align it with body text below.
• Chevrons/arrows following labels: optical gap ≈ 4–6px, less than the grid would suggest.
• Rule of thumb: when something "looks off-center" but the inspector says it's centered, the inspector is wrong. Nudge by 1–2px and re-check by eye (or screenshot).

8. Typography details

• Tabular numbers wherever digits change or align (tables, timers, counters, prices in lists): font-variant-numeric: tabular-nums; — otherwise columns wobble and timers jitter.
• Letter-spacing scales inversely with size: large display text needs negative tracking (-0.01em to -0.03em above ~32px); small ALL-CAPS labels need positive tracking (0.04em–0.08em). Body text: none.
• text-wrap: balance on headings (≤4 lines); text-wrap: pretty on paragraphs to prevent orphan words.
• Font smoothing: on macOS, light-on-dark text renders heavy; -webkit-font-smoothing: antialiased; -moz-osx-font-smoothing: grayscale; slims it. Apply globally on dark UIs; use judgment on light ones.
• Line-height pairs inversely with size: body 1.5–1.65, headings 1.1–1.2, giant display 0.95–1.05.
• Truncation: single line text-overflow: ellipsis; white-space: nowrap; overflow: hidden;; multi-line -webkit-line-clamp. Always add title or a tooltip for truncated content.
• Hyphens/overflow-wrap: anywhere on user-generated strings so long tokens can't blow layouts.
• Interpolate font-variation-settings/weight rather than swapping weights on hover (weight-swap causes width jump; if you must, reserve width with a bold hidden twin).

9. Image treatment

• Subtle inset outline stops light images from bleeding into light backgrounds:

.img-frame { position: relative; }
.img-frame::after {
  content: ""; position: absolute; inset: 0; border-radius: inherit;
  box-shadow: inset 0 0 0 1px rgba(16, 24, 40, 0.08);
  pointer-events: none;
}

• Reserve space to kill layout shift: always set width/height attributes or aspect-ratio on the container; object-fit: cover for fills.
• Background-color placeholder (background: var(--surface-2)) behind every image so slow loads show a designed surface, not a void.
• Avatars: add the inset ring above plus a background color for missing images; never let a broken-image glyph render.
• Hover zoom belongs inside an overflow: hidden frame: image scales 1→1.03–1.05, frame stays put.
• loading="lazy" below the fold; never on the LCP/hero image.

10. Scroll behavior

• scroll-margin-top on anchor targets so sticky headers don't cover them: [id] { scroll-margin-top: calc(var(--header-h) + 16px); }
• scroll-behavior: smooth for in-page anchors — gate it behind reduced-motion (see §11).
• Horizontal scrollers (chip rows, card rails): scroll-snap-type: x mandatory + scroll-snap-align: start, hide scrollbar only if arrows/affordances exist, add overscroll-behavior-x: contain.
• Modals/drawers: lock body scroll while open (overflow: hidden on body or overscroll-behavior: contain on the panel) — background scroll bleed feels broken.
• Custom scrollbars: thin and unobtrusive is fine (scrollbar-width: thin; scrollbar-color: var(--border) transparent); never remove scrollbars from long content.
• Scroll-triggered reveals: threshold ~0.15–0.25, animate once, never re-hide on scroll-up:

const io = new IntersectionObserver((entries) => {
  for (const e of entries) if (e.isIntersecting) { e.target.classList.add("in"); io.unobserve(e.target); }
}, { threshold: 0.2 });
document.querySelectorAll("[data-reveal]").forEach((el) => io.observe(el));

11. Reduced motion

Non-negotiable. Every animation added by this pass must respect prefers-reduced-motion.

@media (prefers-reduced-motion: reduce) {
  *, *::before, *::after {
    animation-duration: 0.01ms !important;
    animation-iteration-count: 1 !important;
    transition-duration: 0.01ms !important;
    scroll-behavior: auto !important;
  }
}

• The blanket rule above is the safety net; prefer targeted alternatives where motion carries meaning (e.g. keep the fade, drop the movement).
• In JS animation code, check matchMedia("(prefers-reduced-motion: reduce)").matches before starting loops, parallax, or auto-playing sequences.
• Opacity fades are generally safe under reduced motion; large translations, scaling, parallax, and auto-scroll are not.

Final pass checklist

• All interactive elements: hover, active, focus-visible, disabled states present and distinct.
• No transition: all; all durations ≤300ms in-app; exits faster than entrances.
• Entering elements fade+move ≤16px; ephemerals originate from their trigger.
• First-load lists stagger ≤60ms/item, capped.
• Shadows layered and tinted; borders on static, shadows on floating; dark mode uses surface steps.
• Nested radii follow inner = outer − padding.
• Icon/text alignment checked by eye, not just by flexbox.
• Tabular nums on data; tracking tightened on display, widened on caps labels; headings balanced.
• Images: aspect-ratio reserved, placeholder background, inset outline where needed.
• Anchor scroll-margin set; body locked under modals; reveals fire once.
• prefers-reduced-motion handled globally and in JS.