Great interfaces rarely come from a single thing. It's usually a collection of small details that compound into a great experience. Apply these principles when building or reviewing UI code.
When reviewing, slow the interface down: replay motion at 10% speed in the browser's Animations panel and walk every state: hover, focus, active, loading, empty. What feels off at 10% speed is what's subtly wrong at full speed.
Preserve the project's component library, tokens, and density. Match its established motion language except where a principle below prescribes an exact interaction pattern.
Typography (text wrapping, font rendering, tabular numbers, spacing) is covered by the better-typography skill; use that for anything text-related. Accessibility (hit areas, focus states, keyboard support, ARIA, reduced-motion requirements) is covered by the better-accessibility skill. Layout structure (grouping, spacing between sections, breakpoints, spatial RTL including icon mirroring) is covered by the better-layout skill. When any of those skills is unavailable, do not stop: apply the project's own tokens and component conventions, fall back to platform defaults where it has none, and record which domain went uncovered so the gap is visible.
The principles below give exact component-level recipes and are self-sufficient. For the project's broader motion vocabulary — easing-curve selection, duration scales, and spring physics reasoning — the emil-design-eng skill goes deeper if it is installed; prefer it when choosing a curve, and use the values here when implementing the specific patterns named below. If it is not available, the values here stand on their own.
Quick Reference
| Category | When to Use |
|---|---|
| Surfaces | Border radius, optical alignment, shadows, image outlines |
| Animations | Interruptible animations, enter/exit transitions, icon animations, scale on press, motion restraint |
| Icons | Icon stroke weight, states via currentColor, outline vs fill, sizing |
| Performance | Transition specificity, will-change usage |
Core Principles
1. Concentric Border Radius
Outer radius = inner radius + padding. Mismatched radii on nested elements is the most common thing that makes interfaces feel off.
2. Optical Over Geometric Alignment
When geometric centering looks off, align optically with an exact offset. A button with a leading icon takes 2px less padding on the icon side than the text side. A play triangle inside a circular button shifts 2px toward the trailing edge, because its visual mass sits left of its bounding box. Asymmetric icons follow the same rule: offset toward the heavier side.
3. Shadows for Elevation, Borders for Structure
For buttons, cards, and containers whose border exists only to create depth, use three layered transparent shadows rather than one: a 1px hairline for the edge, a short blur for contact, and a longer blur for lift — for example 0 1px 0 oklch(0 0 0 / 0.05), 0 1px 2px oklch(0 0 0 / 0.06), 0 4px 12px oklch(0 0 0 / 0.08). Keep borders that communicate structure or state: dividers, layout separators, and selected or focus states.
4. Interruptible Animations
Use CSS transitions for interactive state changes: they can be interrupted mid-animation. Reserve keyframes for staged sequences that run once.
5. Split and Stagger Enter Animations
For an infrequent staged entrance where sequence helps communicate hierarchy, break content into semantic chunks and stagger them by ~100ms instead of animating one container. Do not stagger routine, high-frequency interactions.
6. Subtle Exit Animations
Use a small fixed translateY (-12px) instead of the full container height, and keep the exit shorter than the enter: 150ms out against 300ms in. Use ease-out for both.
7. Contextual Icon Animations
Animate icons with opacity, scale, and blur instead of toggling visibility. Use exactly these values: scale from 0.25 to 1, opacity from 0 to 1, blur from 4px to 0px. If the project has motion or framer-motion in package.json, match that package's import path (or the established nearby imports when both exist) and use transition: { type: "spring", duration: 0.3, bounce: 0 }; bounce must always be 0. If no motion library is installed, keep both icons in the DOM (one absolute-positioned) and cross-fade with CSS transitions using cubic-bezier(0.2, 0, 0, 1); this gives both enter and exit animations without any dependency.
8. Image Outlines
Add a subtle 1px outline with low opacity to images for consistent depth. The color must be pure black in light mode (oklch(0 0 0 / 0.1)) and pure white in dark mode (oklch(1 0 0 / 0.1)), never a near-black like slate, zinc, or any tinted neutral. A tinted outline picks up the surface color underneath it and reads as dirt on the image edge.
9. Scale on Press
A subtle scale on click gives buttons tactile feedback. Use 0.96 when there is nothing else to follow; 0.95–0.97 all read as a press and the difference is imperceptible, so a project's own motion system or a sibling skill's value wins over this one. What matters is the floor: never go below 0.95, where the press starts to read as a bounce.
Apply it consistently — a page where some buttons respond to press and others don't feels broken in a way no single button does. Add a static prop to disable it where motion would be distracting.
10. Skip Animation on Page Load
Use initial={false} on AnimatePresence to prevent enter animations on first render. Verify it doesn't break intentional entrance animations.
11. Never Use transition: all
Always specify exact properties: transition-property: scale, opacity. Tailwind's transition-transform covers transform, translate, scale, rotate.
12. Use will-change Sparingly
Only for transform, opacity, filter, the properties the GPU can composite. Never use will-change: all. Only add when you notice first-frame stutter.
13. Match Icon Stroke to Text Weight
An icon next to text carries the text's optical weight: 1.5px stroke beside regular (400) text, 2px beside semibold (600). One stroke weight per icon set; never mix libraries on one surface.
14. One SVG, Recolored per State
Icons use currentColor and get their states (hover, selected, disabled) from CSS color and opacity, never from separate assets. Outline variant is the default; fill variant marks the active state.
15. Hover Is a Hint, Not a Channel
Hover exists on pointer devices only, so it can reinforce an affordance but never carry information or an action that has no other path. A control revealed only on hover is unreachable by touch and by keyboard.
Make the hovered state a small, fast change — background-color, border-color, or opacity at ≤150ms — not an entrance animation, because hover fires constantly. Give every hover state a :focus-visible equivalent so keyboard users get the same affordance, and gate hover styling on @media (hover: hover) so touch devices don't get a sticky hover stuck after a tap.
Row and card actions that appear on hover are the common trap: keep them present but muted, or reveal them on :focus-within as well, so they exist for every input method.
16. Reach for Modern CSS Only Where It Is Supported
Three primitives replace long-standing workarounds, but they are not one uniformly safe category. Check the project's browser targets before relying on any of them, and say which you assumed.
@starting-stylewithtransition-behavior: allow-discreteanimates an element entering fromdisplay: noneor the top layer, which previously needed JS. Baseline 2024 (Chrome 117, Firefox 129, Safari 17.4–17.5). Support for individual discrete properties such asdisplayis narrower than the feature itself.- Same-document View Transitions are Baseline 2025 (Chrome 111, Firefox 144, Safari 18). Cross-document transitions are not Baseline — treat them as progressive enhancement.
interpolate-size: allow-keywordsandcalc-size()finally animate to and fromautoheight. Both are Chromium-only as of Chrome 129, with no shipped Firefox or Safari support, so they do not yet replace the fixedtranslateYapproach in Principle 6. Use them behind@supportswith a working fallback.
The rule for all three: enhancement, never the only path. If the interaction breaks without the feature, it isn't an enhancement.
17. Motion Restraint
No custom animation on high-frequency interactions: the attention cost repeats on every trigger. Motion is never the only feedback channel; every animated state change also needs a static cue (color, icon, label).
Common Mistakes
| Mistake | Fix |
|---|---|
| Same border radius on closely nested parent and child | Calculate outerRadius = innerRadius + padding |
| Icons look off-center | Adjust optically with padding or fix SVG directly |
| Border used only to fake elevation | Use layered box-shadow with transparency; keep structural and state borders |
| Jarring staged entrance or contextual exit | Stagger infrequent entrances and keep context-preserving exits subtle |
| Stateful icon or toggle animates its default state on page load | Add initial={false} to that AnimatePresence; preserve intentional page entrances |
transition: all on elements |
Specify exact properties |
| First-frame animation stutter | Add will-change: transform (sparingly) |
| Hairline icon beside bold text | Match the stroke width to the text weight |
| Separate icon assets per state | One currentColor SVG, states via CSS |
| Filled icons everywhere | Outline as default, fill only for the active state |
| Action visible only on hover | Keep it present but muted, or also reveal on :focus-within |
Hover state with no :focus-visible equivalent |
Mirror every hover affordance for keyboard |
| Hover styles applied on touch devices | Gate them behind @media (hover: hover) |
interpolate-size or calc-size() used as the only path |
Chromium-only today; put it behind @supports with a fallback |
| Entrance animation on every hover or keystroke | Instant feedback or ≤150ms opacity/color transition |
Severity
HIGHmakes an interaction misleading, unresponsive, or repeatedly disruptive.MEDIUMcreates a noticeable craft or consistency problem.LOWis isolated polish.
Review Output Format
Use this format only when the user asks for a standalone UI-polish review. When better-interface orchestrates the review, provide domain evidence and findings to that skill and let its output format, severity scale, consolidation rules, cap, and verdict take precedence.
Present the standalone review in two parts.
Findings
Group all confirmed findings by principle. Use a markdown table with Severity, Location, Before, After, and Why columns. Never use separate "Before:" / "After:" lines.
- Location: cite
path/to/file:line. If the artifact has no source files, cite the exact screen and component instead. - Before / After: show the current implementation and an actionable replacement.
- Why: name the violated principle and explain how it affects the interface.
Consolidate a repeated systemic issue into one row and list every affected location. Omit principles with no findings.
Example
Concentric border radius
| Severity | Location | Before | After | Why |
|---|---|---|---|---|
| LOW | src/Card.tsx:28 |
rounded-xl on card + rounded-xl on inner button (p-2) |
rounded-2xl on card (8 + 8 = 16), rounded-lg on inner button |
Nested corners should be concentric |
| LOW | src/card.css:11 |
border-radius: 16px on both nested surfaces |
Outer 24px, inner 16px with 8px padding |
Equal nested radii make the inner surface look pinched |
Scale on press
| Severity | Location | Before | After | Why |
|---|---|---|---|---|
| LOW | src/Button.tsx:19 |
<button className="..."> |
Add active:scale-[0.96] transition-transform |
Press feedback makes the control feel responsive |
| MEDIUM | src/button.css:24 |
scale(0.9) on press |
Raise to scale(0.96) |
Anything below 0.95 feels exaggerated |
Verification and Verdict
After the findings:
- Verification: list the exact checks run and their observed results. Walk every relevant state and inspect motion at 10% speed when animation is involved. If a check was not run, state what still needs verification.
- Verdict:
Blockif anyHIGHfinding remains,Needs changesif onlyMEDIUMorLOWfindings remain, andApproveonly when no actionable findings remain.
When there are no findings, omit the tables, state "No actionable UI-polish findings", report verification, and end with Approve.