Emil's Design Engineering Principles
A comprehensive guide for building polished, accessible web interfaces based on Emil Kowalski's design engineering practices.
Quick Reference
| Category |
When to Use |
| Animations |
Enter/exit transitions, easing, springs, performance |
| UI Polish |
Typography, visual design, layout, colors |
| Forms & Controls |
Inputs, buttons, form submission |
| Touch & Accessibility |
Mobile, touch devices, keyboard nav, a11y |
| Component Design |
Compound components, composition, props API |
| Marketing |
Landing pages, blogs, docs sites |
| Performance |
Virtualization, preloading, optimization |
| Design Rules |
Paired right/wrong calls across icons, type, color, IA, interaction, copy |
Core Principles
1. No Layout Shift
Dynamic elements should cause no layout shift. Use hardcoded dimensions, font-variant-numeric: tabular-nums for changing numbers, and avoid font weight changes on hover/selected states.
2. Touch-First, Hover-Enhanced
Design for touch first, then add hover enhancements. Disable hover effects on touch devices. Ensure 44px minimum tap targets. Never rely on hover for core functionality.
3. Keyboard Navigation
Tabbing should work consistently. Only allow tabbing through visible elements. Ensure keyboard navigation scrolls elements into view with scrollIntoView().
4. Accessibility by Default
Every animation needs prefers-reduced-motion support. Every icon button needs an aria label. Every interactive element needs proper focus states.
5. Speed Over Delight
Product UI should be fast and purposeful. Skip animations for frequently-used interactions. Marketing pages can be more elaborate.
Decision Flowcharts
Should I Animate This?
Will users see this 100+ times daily?
├── Yes → Don't animate
└── No
├── Is this user-initiated?
│ └── Yes → Animate with ease-out (150-250ms)
└── Is this a page transition?
└── Yes → Animate (300-400ms max)
What Easing Should I Use?
Is the element entering or exiting?
├── Yes → ease-out
└── No
├── Is it moving on screen?
│ └── Yes → ease-in-out
└── Is it a hover/color change?
├── Yes → ease
└── Default → ease-out
Common Mistakes
| Mistake |
Fix |
transition: all |
Specify exact properties |
| Hover effects on touch |
Use @media (hover: hover) |
| Font weight change on hover |
Use consistent weights |
Animating height/width |
Use transform and opacity only |
| No reduced motion support |
Add prefers-reduced-motion query |
| z-index: 9999 |
Use fixed scale or isolation: isolate |
| Custom page scrollbars |
Only customize scrollbars in small elements |
Review Checklist
When reviewing UI code, check:
Reference Files
For detailed guidance on specific topics:
- animations.md - Easing, timing, springs, performance
- ui-polish.md - Typography, shadows, gradients, scrollbars
- forms-controls.md - Inputs, buttons, form patterns
- touch-accessibility.md - Touch devices, keyboard nav, a11y
- component-design.md - Compound components, composition, props API
- marketing.md - Landing pages, blogs, docs
- performance.md - Virtualization, preloading, optimization
1---2name: emil-design-engineering3description: Design engineering principles and patterns for building polished, accessible web interfaces. Use this skill when building UI components, reviewing frontend code, implementing forms, handling touch interactions, optimizing performance, or creating marketing pages. Triggers on: design engineering, UI polish, input fields, form validation, button states, touch devices, mobile UX, accessibility, a11y, keyboard navigation, aria labels, font rendering, typography, layout shift, z-index, animations, transitions, easing, hover effects, tap targets, iOS Safari, prefers-reduced-motion, marketing pages, landing pages, dark mode, theme switching, scrollbars, gradients, shadows, virtualization, preloading.4---56# Emil's Design Engineering Principles78A comprehensive guide for building polished, accessible web interfaces based on Emil Kowalski's design engineering practices.910## Quick Reference1112| Category | When to Use |13| ----------------------------------------------- | ------------------------------------------------------------------------- |14| [Animations](animations.md) | Enter/exit transitions, easing, springs, performance |15| [UI Polish](ui-polish.md) | Typography, visual design, layout, colors |16| [Forms & Controls](forms-controls.md) | Inputs, buttons, form submission |17| [Touch & Accessibility](touch-accessibility.md) | Mobile, touch devices, keyboard nav, a11y |18| [Component Design](component-design.md) | Compound components, composition, props API |19| [Marketing](marketing.md) | Landing pages, blogs, docs sites |20| [Performance](performance.md) | Virtualization, preloading, optimization |21| [Design Rules](design-rules.md) | Paired right/wrong calls across icons, type, color, IA, interaction, copy |2223## Core Principles2425### 1. No Layout Shift2627Dynamic elements should cause no layout shift. Use hardcoded dimensions, `font-variant-numeric: tabular-nums` for changing numbers, and avoid font weight changes on hover/selected states.2829### 2. Touch-First, Hover-Enhanced3031Design for touch first, then add hover enhancements. Disable hover effects on touch devices. Ensure 44px minimum tap targets. Never rely on hover for core functionality.3233### 3. Keyboard Navigation3435Tabbing should work consistently. Only allow tabbing through visible elements. Ensure keyboard navigation scrolls elements into view with `scrollIntoView()`.3637### 4. Accessibility by Default3839Every animation needs `prefers-reduced-motion` support. Every icon button needs an aria label. Every interactive element needs proper focus states.4041### 5. Speed Over Delight4243Product UI should be fast and purposeful. Skip animations for frequently-used interactions. Marketing pages can be more elaborate.4445## Decision Flowcharts4647### Should I Animate This?4849```50Will users see this 100+ times daily?51├── Yes → Don't animate52└── No53 ├── Is this user-initiated?54 │ └── Yes → Animate with ease-out (150-250ms)55 └── Is this a page transition?56 └── Yes → Animate (300-400ms max)57```5859### What Easing Should I Use?6061```62Is the element entering or exiting?63├── Yes → ease-out64└── No65 ├── Is it moving on screen?66 │ └── Yes → ease-in-out67 └── Is it a hover/color change?68 ├── Yes → ease69 └── Default → ease-out70```7172## Common Mistakes7374| Mistake | Fix |75| --------------------------- | ------------------------------------------- |76| `transition: all` | Specify exact properties |77| Hover effects on touch | Use `@media (hover: hover)` |78| Font weight change on hover | Use consistent weights |79| Animating `height`/`width` | Use `transform` and `opacity` only |80| No reduced motion support | Add `prefers-reduced-motion` query |81| z-index: 9999 | Use fixed scale or `isolation: isolate` |82| Custom page scrollbars | Only customize scrollbars in small elements |8384## Review Checklist8586When reviewing UI code, check:8788- [ ] No layout shift on dynamic content89- [ ] Animations have reduced motion support90- [ ] Touch targets are 44px minimum91- [ ] Hover effects disabled on touch devices92- [ ] Keyboard navigation works properly93- [ ] Icon buttons have aria labels94- [ ] Forms submit with Enter/Cmd+Enter95- [ ] Inputs are 16px+ to prevent iOS zoom96- [ ] No `transition: all`97- [ ] z-index uses fixed scale9899## Reference Files100101For detailed guidance on specific topics:102103- [animations.md](animations.md) - Easing, timing, springs, performance104- [ui-polish.md](ui-polish.md) - Typography, shadows, gradients, scrollbars105- [forms-controls.md](forms-controls.md) - Inputs, buttons, form patterns106- [touch-accessibility.md](touch-accessibility.md) - Touch devices, keyboard nav, a11y107- [component-design.md](component-design.md) - Compound components, composition, props API108- [marketing.md](marketing.md) - Landing pages, blogs, docs109- [performance.md](performance.md) - Virtualization, preloading, optimization
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