gabrielmoreira 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.
Quick Reference
| Category | When to Use |
|---|---|
| Typography | Text wrapping, font smoothing, tabular numbers |
| Surfaces | Border radius, optical alignment, shadows, image outlines, hit areas |
| Animations | Interruptible animations, enter/exit transitions, icon animations, scale on press |
| 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. Buttons with icons, play triangles, and asymmetric icons all need manual adjustment.
3. Shadows Over Borders
For elevation (dropdowns, modals, cards) use the shadow-subtle/shadow-medium/shadow-overlay/shadow-card tokens. In this repo neutral edges and dividers stay as --border borders (.claude/rules/sim-styling.md, Line weight) — do not swap them for 0 0 0 1px shadow rings.
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 contextual icons with opacity, scale, and blur instead of toggling visibility; see animations.md for the Motion and CSS cross-fade patterns.
8. Font Smoothing
Apply -webkit-font-smoothing: antialiased to the root layout on macOS for crisper text.
9. Tabular Numbers
Use font-variant-numeric: tabular-nums for any dynamically updating numbers to prevent layout shift.
10. Text Wrapping
Use text-wrap: balance on headings. Use text-wrap: pretty for body text to avoid orphans.
11. Image Outlines
Add a subtle 1px low-opacity outline to images (outline-black/10 light, outline-white/10 dark); see surfaces.md.
12. Scale on Press
A subtle scale-down (about 0.96-0.97) on press gives tactile feedback. In this repo a press affordance belongs in the emcn Button/Chip chrome (packages/emcn), not in consumer classes — neither component implements one today, so propose it there rather than adding per-call-site transforms.
13. 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.
14. Never Use transition: all
Always specify exact properties: transition-property: scale, opacity. Tailwind's transition-transform covers transform, translate, scale, rotate.
15. Use will-change Sparingly
Only for transform, opacity, filter — properties the GPU can composite. Never use will-change: all. Only add when you notice first-frame stutter.
16. Minimum Hit Area
Interactive elements need at least 40×40px hit area. 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 | In this repo, the --border hairline token; elsewhere, layered box-shadow with transparency |
| Jarring enter/exit animations | Split, stagger, and keep exits subtle |
| Numbers cause layout shift | Apply tabular-nums |
| Heavy text on macOS | Apply antialiased to root |
| 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 pseudo-element to 40×40px |
Review Output Format
Present changes as markdown tables with Before and After columns, one table per principle with a heading above it, one diff per row, and cite file and property when the snippet is not self-explanatory.
Example
Concentric border radius
| Before | After |
|---|---|
rounded-xl on card + rounded-xl on inner button (p-2) |
rounded-2xl on card (12 + 8), rounded-lg on inner button |
border-radius: 16px on both nested surfaces |
Outer 24px, inner 16px with 8px padding |
Tabular numbers
| Before | After |
|---|---|
<span>{count}</span> on animated counter |
<span className="tabular-nums">{count}</span> |
| Default numerals on timer | Added font-variant-numeric: tabular-nums to root |
Scale on press
| Before | After |
|---|---|
<button className="..."> |
Added active:scale-[0.96] transition-transform |
scale(0.9) on press |
Raised to scale(0.96) — anything below 0.95 feels exaggerated |
Rows should cite the specific file and the specific property that changed when it isn't obvious from the snippet. If a principle was reviewed but nothing needed to change, omit that table entirely — empty tables add noise.
Review Checklist
- Nested rounded elements use concentric border radius
- Icons are optically centered, not just geometrically
- Shadows used instead of borders where appropriate
- Enter animations are split and staggered
- Exit animations are subtle
- Dynamic numbers use tabular-nums
- Font smoothing is applied
- Headings use text-wrap: balance
- Images have subtle outlines
- Buttons use scale on press where appropriate
- AnimatePresence uses
initial={false}for default-state elements - No
transition: all— only specific properties -
will-changeonly on transform/opacity/filter, neverall - Interactive elements have at least 40×40px hit area
Reference Files
- typography.md — Text wrapping, font smoothing, tabular numbers
- surfaces.md — Border radius, optical alignment, shadows, image outlines
- animations.md — Interruptible animations, enter/exit transitions, icon animations, scale on press
- performance.md — Transition specificity,
will-changeusage