Design engineering principles for polishing UI details
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.
| 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 |
Outer radius = inner radius + padding. Mismatched radii on nested elements is the most common thing that makes interfaces feel off.
When geometric centering looks off, align optically. Buttons with icons, play triangles, and asymmetric icons all need manual adjustment.
Layer multiple transparent box-shadow values for natural depth. Shadows adapt to any background; solid borders don't.
Use CSS transitions for interactive state changes — they can be interrupted mid-animation. Reserve keyframes for staged sequences that run once.
Don't animate a single container. Break content into semantic chunks and stagger each with ~100ms delay.
Use a small fixed translateY instead of full height. Exits should be softer than enters.
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.
Apply -webkit-font-smoothing: antialiased to the root layout on macOS for crisper text.
Use font-variant-numeric: tabular-nums for any dynamically updating numbers to prevent layout shift.
Use text-wrap: balance on headings. Use text-wrap: pretty for body text to avoid orphans.
Add a subtle 1px outline with low opacity to images for consistent depth.
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.
Use initial={false} on AnimatePresence to prevent enter animations on first render. Verify it doesn't break intentional entrance animations.
transition: allAlways specify exact properties: transition-property: scale, opacity. Tailwind's transition-transform covers transform, translate, scale, rotate.
will-change SparinglyOnly for transform, opacity, filter — properties the GPU can composite. Never use will-change: all. Only add when you notice first-frame stutter.
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.
| 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 |
| 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 |
initial={false} for default-state elementstransition: all — only specific propertieswill-change only on transform/opacity/filter, never allwill-change usage