Surface Details

Details

Platform-specific implementation details and visual polish that separate professional web interfaces from amateur ones. Based on the Web Interface Guidelines by Rauno Freiberg and the interface details work of Jakub Królikowski.

This skill fires during construction of interactive elements and when debugging platform behaviour. It is deliberately granular: a list of specific, testable details. For design philosophy, see references/design-philosophy.md. For animation implementation, see surface-motion. For accessibility across all skills, see references/accessibility.md. For multi-skill task sequencing, see references/composition.md.

For native iOS/macOS values (hit targets, type minima, bar metrics, component idiom) use the hig suite — this skill's web values do not apply to prototypes imitating native Apple UI; on conflict there, HIG wins.

For expanded hit areas, safe-area insets, hairline separators, text overflow, hydration flash, platform shortcut labels, and inert inactive regions, read references/interface-polish.md.

Forms and Inputs

Labels focus inputs. Every input has a <label> bound via for/id or wrapping. Clicking the label focuses the input.

Inputs live inside a <form>. Even single-input UIs. This enables Enter to submit.

Set the correct type. email, password, tel, url, search, number. This controls the mobile keyboard layout. The wrong type means the wrong keyboard.

Disable spellcheck by default on most inputs. Only enable where prose is expected (textareas, rich text editors). Leave autocomplete enabled by default. Users with motor and cognitive disabilities, and anyone using a password manager, depend on it. Disable autocomplete only on specific fields where the browser's suggestions are misleading (e.g. a field labelled "email" that asks for someone else's email, or a one-time code input).

Let textareas grow with content when writing is the main task. Avoid nested textarea scrolling by default. Growing textareas create a smoother writing experience and keep forms easier to scan. Use constraints only when the surrounding layout genuinely requires them.

textarea {
  field-sizing: content;
}

Use the required attribute. HTML validation before JavaScript validation. The browser handles it for free.

Position input decorations on top. Icons, currency symbols, and prefix/suffix elements should be absolutely positioned over the input with corresponding padding. Never place them as adjacent siblings. Clicking the decoration must focus the input.

.input-wrapper {
  position: relative;
}

.input-icon {
  position: absolute;
  left: 0.75rem;
  top: 50%;
  transform: translateY(-50%);
  pointer-events: none;
}

.input-field {
  padding-left: 2.5rem;
}

Toggles, Buttons, and Interactive Elements

Toggles take effect immediately. Never require a separate confirmation step for a toggle. If toggling triggers a network request, show a loading state on the toggle itself.

Disable buttons after submission. Prevents duplicate network requests. Re-enable on success or failure.

Use focus rings instead of focus borders. In Tailwind, prefer focus:ring-2 or focus-visible:ring-2 over focus:border-* for buttons and other controls. Changing the border on focus changes the element's box model and can cause layout shift when the user clicks or tabs to it.

user-select: none on interactive content. Prevents accidental text selection during clicks, drags, and taps. Apply to the inner content of buttons, toggles, tabs, and drag handles.

pointer-events: none on decorative elements. Glows, gradients, particle effects, and overlays must not intercept clicks or hover events.

No dead zones between list items. In a list of clickable items, increase padding to fill the space rather than using margin or gap. Every pixel between items should be clickable by one of them.

/* Wrong: gap creates unclickable dead zones */
.list { display: flex; flex-direction: column; gap: 8px; }
.list-item { padding: 8px; }

/* Right: padding fills the space */
.list { display: flex; flex-direction: column; }
.list-item { padding: 12px; }  /* extra padding absorbs the gap */

Extend small hit areas. Icon buttons, checkboxes, and drag handles that are visually smaller than 44px need a pseudo-element or wrapping label to enlarge the target. Expanded hit areas must not overlap neighbouring controls.

Dropdown and Context Menus

Open on mousedown, not click. click waits for both press and release, adding ~100ms of perceived latency. mousedown fires on press, making menus feel instant.

Prediction cone for nested menus. When a top-level menu item reveals a submenu, the user moves the pointer diagonally toward it. Without a prediction cone (safe triangle), the pointer crosses other menu items and triggers their submenus instead, closing the intended one. Implement a triangular hit area between the current pointer position and the submenu bounds.

Tooltips

Skip delay on subsequent tooltips. Tooltips should have a slight delay (200-300ms) before appearing to prevent accidental activation. But once a tooltip is open, hovering over another tooltip trigger should show it immediately with no delay and no animation. This feels faster without defeating the purpose of the initial delay.

Radix and Base UI handle the delay skipping automatically. Base UI also supports skipping the animation via the data-instant attribute:

.tooltip {
  transition: transform 125ms ease-out, opacity 125ms ease-out;
  transform-origin: var(--transform-origin);
}

.tooltip[data-starting-style],
.tooltip[data-ending-style] {
  opacity: 0;
  transform: scale(0.97);
}

/* Skip animation on subsequent tooltips */
.tooltip[data-instant] {
  transition-duration: 0ms;
}

Touch

Scope hover styles to pointer devices.

@media (hover: hover) {
  .button:hover { background: var(--color-surface-hover); }
}

Without this, touch devices show a persistent "sticky hover" state after tap.

Input font size minimum 16px. Any <input> or <textarea> with font-size below 16px triggers automatic page zoom on focus in iOS Safari. This is the single most common mobile bug.

Never auto-focus inputs on touch devices. Auto-focus opens the virtual keyboard immediately, covering half the screen before the user has oriented themselves. On desktop, auto-focus is fine.

Video autoplay on iOS. Add muted and playsinline attributes to <video> tags. Without both, autoplay will not work.

<video autoplay muted playsinline loop>
  <source src="hero.mp4" type="video/mp4">
</video>

Disable native gestures on custom gesture areas. For components with custom pan, pinch, or zoom behaviour, set touch-action: none to prevent the browser's native gestures from interfering.

Replace the iOS tap highlight. Disable the default with -webkit-tap-highlight-color: transparent, but always add a visible active/pressed state as replacement. Removing the highlight without an alternative is an accessibility regression.

Respect safe areas. Fixed mobile UI uses env(safe-area-inset-*) so bottom bars, toasts, drawers, and floating actions do not collide with notches, home indicators, or browser chrome.

Scroll

Smooth scroll for anchors.

html { scroll-behavior: smooth; }

[id] { scroll-margin-top: 5rem; }  /* account for fixed header */

Pause off-screen loops. Looping animations (CSS or JS) and auto-playing videos should pause when scrolled out of view. Use IntersectionObserver to detect visibility. This saves CPU and GPU.

Performance

Large blur() values are expensive. filter: blur() and backdrop-filter: blur() with high values (20px+) cause visible performance drops on lower-end devices. Test on real hardware. Reduce or remove blur on prefers-reduced-motion: reduce.

Blurred rectangles cause banding. Scaling and blurring a solid-colour rectangle produces visible colour banding. Use radial-gradient instead.

GPU compositing as last resort. transform: translateZ(0) forces GPU compositing and can fix janky animations. But apply it sparingly and only to the specific element. Pre-emptively adding it to many elements wastes GPU memory.

will-change only during animation. Apply will-change for the duration of an active animation, then remove it. Adding it permanently to static elements reserves GPU resources for nothing and can make performance worse.

Limit concurrent videos on iOS. Auto-playing too many <video> elements simultaneously chokes iOS devices. Pause or unmount videos that scroll out of view.

Bypass React rendering for real-time values. For scroll position, pointer coordinates, and animation frames, track values in a ref and write directly to the DOM. Pushing high-frequency updates through React state causes unnecessary re-renders.

const scrollY = useRef(0);

useEffect(() => {
  const handler = () => {
    scrollY.current = window.scrollY;
    elementRef.current.style.transform = `translateY(${scrollY.current * 0.5}px)`;
  };
  window.addEventListener('scroll', handler, { passive: true });
  return () => window.removeEventListener('scroll', handler);
}, []);

Accessibility Micro-Details

Disabled buttons have no tooltips. Disabled elements are removed from the tab order. Screen reader and keyboard users will never discover the tooltip. Show inline text explaining why the button is disabled instead.

Focus rings follow border-radius. Use box-shadow for custom focus rings if you need to support older Safari (pre-16.4) where outline ignores radius. On modern browsers, outline with outline-offset works.

Inactive regions leave focus navigation. Hidden menus, closed drawers, inactive tab panels, and background pages behind modals should not remain reachable by Tab. Use focus trapping for modals and inert where supported.

Arrow keys navigate sequential lists. Focusable elements in a vertical list support ↑/↓ navigation (roving tabindex). In a horizontal list, ←/→.

⌘+Backspace deletes in lists. Keyboard users expect to delete a focused list item without reaching for a button.

aria-label on icon-only elements. Every icon button, icon link, and icon toggle needs an explicit label. Use system-naming when choosing the label text.

Tooltips are informational only. Hover-triggered tooltips must not contain interactive content (links, buttons). Interactive content goes in a popover.

Images use <img>, not background-image. Screen readers can access <img> with alt text. background-image is invisible to assistive tech and cannot be right-click copied.

Decorative HTML is hidden from assistive tech. Purely decorative DOM gets aria-hidden="true" and must not receive focus. Meaningful non-text illustrations or effects need an accessible name, caption, or nearby text that communicates their purpose.

Gradient text selection.

.gradient-text::selection {
  -webkit-background-clip: unset;
  background: var(--color-selection);
  color: var(--color-on-selection);
}

Without this, selecting gradient text produces unreadable results.

Implementation Patterns

Optimistic updates. Update the UI immediately on action. Roll back with feedback if the server errors. Never show a spinner for actions that succeed 99% of the time.

Server-side auth redirects. Authentication redirects happen before the client renders. Client-side redirects cause a flash of the wrong page and a janky URL change.

Style ::selection.

::selection {
  background: var(--color-brand);
  color: var(--color-on-brand);
}

Feedback near its trigger. A copy button shows an inline checkmark, not a toast. Form errors highlight the specific invalid inputs, not a banner at the top. Feedback is always spatially associated with the action that caused it.

Designed empty states. An empty list prompts the user to create their first item. Include a call-to-action and, where appropriate, templates or starting examples.

Theme switching without transition flash. Toggling between light and dark mode must temporarily disable CSS transitions to prevent every element on screen from visibly transitioning. Re-enable transitions after the switch. Libraries like next-themes handle this automatically.

Pause timers when the tab is hidden. Auto-dismissing elements (toasts, banners, notifications) should pause their timers when document.hidden is true. If a toast fires and the user is in another tab, the toast should still be visible when they return. Use the visibilitychange event to pause and resume.

Fill hover gaps with pseudo-elements. When interactive elements have gaps between them (stacked toasts, spaced cards), hovering between items triggers a mouseout. Add ::after pseudo-elements to fill the gaps so the hover state is maintained across the group.

Maintain pointer capture during drag. When a user drags an element (a toast, a slider thumb, a card), set pointer capture on pointerdown so the element continues receiving events even if the pointer leaves its bounds. Without this, fast drags lose tracking when the cursor escapes the element.

Quality-of-Life Papercuts

These details rarely define the core feature, but they strongly affect whether the interface feels trustworthy.

Preserve entered data by default. Unless the user explicitly discards it, information they entered should survive navigation, validation errors, modal closes, and temporary network failure. If preservation is not possible, warn before data is lost.

Maintain subjective scroll position. When items are added to or removed from a list above the viewport, adjust scroll offset so visible items stay visually anchored. Do not make the user's place jump because data changed.

Keep edit-mode text stable. When static text becomes editable, keep the text in the same visual position. The cursor, field padding, font size, and line-height should match the display state closely enough that the mode switch feels continuous.

Place popovers safely under the cursor. If a click opens a new surface at the pointer location, do not put a destructive or risky action under the same cursor position. A double click or accidental second tap must not trigger a dangerous action.

Keep context menu actions stable. Open context menus so actions appear in a predictable position relative to the cursor. Reposition for viewport bounds without changing the internal order or placing common actions in surprising locations.

Add coyote time to multi-key shortcuts. For shortcuts that involve multiple keys, allow a small release grace period so the command is not cancelled the instant the user releases one key slightly early.

Snap movable elements to natural positions. Carousels, horizontal stacks, drawers, sliders, and segmented draggable surfaces should settle into meaningful positions instead of stopping at arbitrary offsets.

Preview changes live. When settings affect visible output, show the change immediately. If the target is off-screen or hidden, show a local preview near the controls.

Visual Polish

Concentric border radius. When nesting a rounded element inside a rounded container, the outer radius must equal the inner radius plus the padding between them. Mismatched radii are one of the most visible signs of careless UI work.

/* outer radius = inner radius + padding */
.card       { border-radius: 20px; padding: 8px; }
.card-inner { border-radius: 12px; }  /* 20 - 8 = 12 */

If the padding changes, the inner radius must change with it. This relationship is not optional.

Optical alignment over geometric alignment. Geometric centering (equal padding on all sides) sometimes looks visually unbalanced. When an element contains both text and an icon, the icon side typically needs less padding than the text side to appear optically centred.

/* Geometric: equal padding, looks off */
.button { padding: 0 16px; }

/* Optical: less padding on the icon side */
.button-with-leading-icon  { padding: 0 16px 0 12px; }
.button-with-trailing-icon { padding: 0 12px 0 16px; }

Play/arrow icons are the worst offenders. If alignment looks wrong despite correct measurements, trust the eye and adjust by 2-4px.

Surface edge plus elevation instead of flat borders. Crisp surface definition and elevation are separate jobs. Use an edge token for the surface boundary, then add elevation only when the element should feel raised.

Use system-tokens's edge tokens (--edge-surface, --edge-surface-strong) for definition and shadow scale (--shadow-sm through --shadow-xl) for depth. The composed semantic aliases (--shadow-card, --shadow-dropdown, --shadow-modal) should normally include both.

.surface {
  box-shadow: var(--edge-surface);
}

.card {
  box-shadow: var(--shadow-card);
}

Use this on cards, popovers, toolbars, floating buttons, raised controls, sheets, and menus. Do not use it as a replacement for real separators, table gridlines, input outlines, or focus rings.

For hover states, keep the edge token stable and step up one elevation level or slightly increase shadow opacity (e.g. 0.06 to 0.08). Add transition: box-shadow to animate between states.

Image outline for depth. A 1px semi-transparent outline on images creates a subtle sense of containment and depth, particularly in design systems where other elements also have borders.

.image {
  outline: 1px solid rgba(0, 0, 0, 0.1);
  outline-offset: -1px;
}

.dark .image {
  outline-color: rgba(255, 255, 255, 0.1);
}

Anti-Patterns

1. iOS input zoom. Input font size below 16px. The single most common mobile bug.
2. Sticky hover on touch. Not using @media (hover: hover).
3. Dead zones in lists. Margin or gap instead of padding between clickable items.
4. Auto-focus on mobile. Opening the keyboard before the user is ready.
5. Toast for important feedback. Copy confirmation, form success, and errors should be inline.
6. will-change on everything. Wastes GPU memory and can reduce performance.
7. Outline focus rings on rounded elements. Outline doesn't follow radius in older browsers.
8. Disabled button with tooltip. Keyboard users will never see it.
9. Mismatched nested border radii. Inner and outer radius are the same value instead of outer = inner + padding.
10. Geometric alignment with icons. Equal padding on a button with an icon. The icon side needs less padding to look centred.
11. Losing entered data. Navigation, validation, or network failure clears what the user already typed.
12. Jumping scroll position. List mutations move visible content unexpectedly.
13. Risky action under cursor. A newly opened menu places destructive action below the current pointer.
14. Nested scrolling in writing textareas. Fixed-height textareas make longer writing harder to scan. Prefer content-sized textareas unless the layout truly needs a fixed editor region.

Checklist

Inputs

• Labels focus their input
• Inputs inside a <form>
• Correct type attributes
• Textareas grow with content when writing is the main task
• Decorations positioned on top, not adjacent
• Font size at least 16px (iOS zoom)

Touch

• Hover scoped to @media (hover: hover)
• iOS tap highlight replaced with active state
• No auto-focus on touch devices
• Videos have muted playsinline
• Custom gesture areas set touch-action: none

Performance

• Off-screen videos and loops paused
• will-change only during active animation
• Large blur tested on real hardware
• Real-time values use refs, not state

Accessibility

• Disabled buttons have inline explanation, not tooltip
• Focus rings visible and follow radius
• Focus styles use rings or outline, not border changes that shift layout
• Inactive regions are not reachable by Tab
• Icon-only buttons have aria-label
• Arrow key navigation in sequential lists
• ::selection styled
• Gradient text readable when selected

Implementation

• Optimistic updates with rollback
• Auth redirects server-side
• Empty states prompt creation
• Feedback inline near trigger
• Theme switching suppresses transitions
• Persisted UI state does not flash after hydration
• Auto-dismiss timers pause when tab is hidden
• Hover gaps filled with pseudo-elements
• Pointer capture set on drag start

Quality-of-Life

• Entered data preserved unless explicitly discarded
• List mutations maintain subjective scroll position
• Edit-mode text stays visually stable
• Risky actions are not placed under the current cursor
• Context menu actions stay predictably positioned
• Multi-key shortcuts include coyote time where useful
• Movable elements snap to natural positions
• Settings changes preview live or near the controls

Tooltips

• Initial delay before first tooltip (200-300ms)
• Subsequent tooltips skip delay and animation

Visual Polish

• Nested border radii are concentric (outer = inner + padding)
• Buttons with icons use optical alignment (reduced padding on icon side)
• Elevated surfaces compose an edge token for crisp definition with a shadow token for depth
• Edge tokens are not used as table borders, dividers, input outlines, or focus rings
• Images have a subtle pure black or white alpha outline for containment
• Fixed mobile UI respects safe-area insets

Learning from Usage

After completing a UI implementation task, review the output against the checklist. Append findings to learnings.md in this skill's folder. Installed learnings are local runtime notes preserved across suite updates; consult learnings.md before starting any new task.