# Details that make interfaces feel better

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.

Typography (text wrapping, font smoothing, tabular numbers, spacing) is covered by the `better-typography` skill; use that for anything text-related.

## Quick Reference

| Category | When to Use |
| --- | --- |
| [Surfaces](surfaces.md) | Border radius, optical alignment, shadows, image outlines, hit areas |
| [Animations](animations.md) | Interruptible animations, enter/exit transitions, icon animations, scale on press |
| [Performance](performance.md) | 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. Buttons with icons, play triangles, and asymmetric icons all need manual adjustment.

### 3. Shadows Over Borders

Layer multiple transparent `box-shadow` values for natural depth. Shadows adapt to any background; solid borders don't.

### 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

Don't animate a single container. Break content into semantic chunks and stagger each with ~100ms delay.

### 6. Subtle Exit Animations

Use a small fixed `translateY` instead of full height. Exits should be softer than enters.

### 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`, 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(0.96)` on click gives buttons tactile feedback. Always use `0.96`. Never use a value smaller than `0.95`: anything below feels exaggerated. Add a `static` prop to disable it when 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. Minimum Hit Area

Interactive elements need a 44×44px hit area for touch or mobile contexts. In desktop interfaces, use at least 40×40px. Extend with a pseudo-element if the visible element is smaller. Never let hit areas of two elements overlap.

## Common Mistakes

| Mistake | Fix |
| --- | --- |
| Same border radius on parent and child | Calculate `outerRadius = innerRadius + padding` |
| Icons look off-center | Adjust optically with padding or fix SVG directly |
| Hard borders between sections | Use layered `box-shadow` with transparency |
| Jarring enter/exit animations | Split, stagger, and keep exits subtle |
| Animation plays on page load | Add `initial={false}` to `AnimatePresence` |
| `transition: all` on elements | Specify exact properties |
| First-frame animation stutter | Add `will-change: transform` (sparingly) |
| Tiny hit areas on small controls | Extend with a pseudo-element to 44×44px for touch/mobile, or at least 40×40px in desktop UI |

## Review Output Format

Always present changes as a markdown table with **Before** and **After** columns. Include every change you made, not just a subset. Never list findings as separate "Before:" / "After:" lines outside of a table. Group changes by principle using a heading above each table, and keep each row focused on a single diff so the reader can scan the whole list quickly.

### Example

#### Concentric border radius
| Before | After |
| --- | --- |
| `rounded-xl` on card + `rounded-xl` on inner button

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