/web-ui-best-practices

name: web-ui-best-practices
description: Signs of taste in web UI. Use when building or reviewing any user-facing web interface — dashboards, SaaS apps, marketing sites, internal tools. Covers interaction speed, navigation depth, visual restraint, copy quality, and the small details that separate polished products from rough ones.

Web UI best practices

Principles for building web interfaces that feel fast, intentional, and respectful of the user's time. Every rule here is a smell test — violating one is fine if you have a reason, violating several means the UI needs work.

Speed

Every interaction completes in under 100ms. If it can't, fake it.

• Optimistic UI updates — show the result before the server confirms
• Debounce inputs, but never debounce perceived response
• Prefetch likely next routes on hover or viewport entry
• Use `will-change` and `transform` for animations, never `top`/`left`
• Measure with `performance.now()`, not gut feel

// Optimistic delete — remove from UI immediately, reconcile later
async function handleDelete(id) {
  setItems(prev => prev.filter(i => i.id !== id));
  try {
    await api.delete(`/items/${id}`);
  } catch {
    setItems(prev => [...prev, originalItem]);
    toast("Couldn't delete. Restored.");
  }
}

Skeleton loading states

Never show a spinner when you know the shape of what's coming. Render a skeleton that matches the layout, then swap in real content.

.skeleton {
  background: linear-gradient(90deg, #f0f0f0 25%, #e0e0e0 50%, #f0f0f0 75%);
  background-size: 200% 100%;
  animation: shimmer 1.5s infinite;
  border-radius: 4px;
}

@keyframes shimmer {
  0% { background-position: 200% 0; }
  100% { background-position: -200% 0; }
}

Modern CSS toolkit

Four capabilities matured between 2023 and 2026 that change how you build component-level responsive layouts and SPA-like transitions without JavaScript. Reach for them before adding a framework.

Container queries

Container queries let a component respond to **its container's** size, not the viewport's. The same card can render in a 300px sidebar and a 900px main column without media-query coordination at the page level.

.card-list {
  container-type: inline-size;
  container-name: cards;
}

@container cards (min-width: 480px) {
  .card { display: grid; grid-template-columns: 120px 1fr; }
}

Stable in all major browsers since 2023. Replaces most "the same component in two places needs to look different" hacks.

`:has()` parent selector

`:has()` lets a parent style itself based on its descendants — the long-requested "parent selector." Useful for marking a form field as in-error, a card as having an attached image, or a row as containing a focused input — all without JS.

/* Highlight a form group when its input has focus */
.form-group:has(input:focus) {
  outline: 2px solid var(--color-primary);
}

/* Add bottom margin to articles that contain a figure */
article:has(figure) {
  margin-bottom: 2rem;
}

Stable in Chrome, Safari, and Firefox since late 2023. Cuts a real category of JS-driven class toggling.

View transitions

The View Transitions API animates between two DOM states (route changes, modal open/close, list-item swaps) without a framework. The browser snapshots the old state, swaps in the new state, then crossfades or slides between them.

// Same-document transition (Chrome 111+, Safari TP, Firefox behind a flag)
function navigate(newView) {
  if (!document.startViewTransition) {
    renderView(newView);
    return;
  }
  document.startViewTransition(() => renderView(newView));
}

/* Smooth crossfade by default; override per element */
::view-transition-old(*) { animation-duration: 200ms; }
::view-transition-new(*) { animation-duration: 200ms; }

Cross-document view transitions (between full page navigations) shipped to Chrome 126 in 2024 and let MPAs feel like SPAs. Pair with `prefers-reduced-motion` so users with motion sensitivity get an instant swap, not an animation.

Scroll-driven animations

`animation-timeline: scroll()` and `animation-timeline: view()` drive CSS animations from scroll position instead of wall-clock time. The classic use case is a progress indicator at the top of an article that fills as you scroll.

@keyframes fill { from { transform: scaleX(0); } to { transform: scaleX(1); } }

.read-progress {
  position: fixed; top: 0; left: 0; right: 0; height: 3px;
  background: var(--color-primary);
  transform-origin: left;
  animation: fill linear;
  animation-timeline: scroll(root);
}

Stable in Chromium-based browsers (Chrome 115+, Edge); not yet in Safari or Firefox as of 2026-05. Use as progressive enhancement; provide a JS fallback or accept a less-flashy baseline elsewhere.

No product tours

If you need a tour to explain your UI, the UI is wrong. Instead:

• Empty states that teach by doing ("Create your first project")
• Progressive disclosure — show features when they become relevant
• Inline hints that disappear after first use
• Defaults that work without configuration

URLs

Slugs are short, readable, and human-guessable. No UUIDs, no query param soup.

Good:  /projects/weather-app
       /settings/billing
       /docs/api/auth

Bad:   /projects/550e8400-e29b-41d4-a716-446655440000
       /app?view=settings&tab=billing&subsection=plan
       /dashboard#!/module/documents/list?filter=active

• Use slugs derived from user-provided names
• Keep nesting to 3 segments max
• Make URLs copyable and shareable — they are the product's memory

Persistent resumable state

Users leave and come back. Respect that.

• Save draft form state to `localStorage` or the server
• Restore scroll position on back navigation
• Preserve filter/sort selections across sessions
• URL encodes the current view state — sharing a URL reproduces the view

// Persist form state across sessions
function usePersistentForm(key, defaults) {
  const [state