---
name: emil-design-engineering
description: "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."
---

# 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](animations.md)                     | Enter/exit transitions, easing, springs, performance                      |
| [UI Polish](ui-polish.md)                       | Typography, visual design, layout, colors                                 |
| [Forms & Controls](forms-controls.md)           | Inputs, buttons, form submission                                          |
| [Touch & Accessibility](touch-accessibility.md) | Mobile, touch devices, keyboard nav, a11y                                 |
| [Component Design](component-design.md)         | Compound components, composition, props API                               |
| [Marketing](marketing.md)                       | Landing pages, blogs, docs sites                                          |
| [Performance](performance.md)                   | Virtualization, preloading, optimization                                  |
| [Design Rules](design-rules.md)                 | 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:

- [ ] No layout shift on dynamic content
- [ ] Animations have reduced motion support
- [ ] Touch targets are 44px minimum
- [ ] Hover effects disabled on touch devices
- [ ] Keyboard navigation works properly
- [ ] Icon buttons have aria labels
- [ ] Forms submit with Enter/Cmd+Enter
- [ ] Inputs are 16px+ to prevent iOS zoom
- [ ] No `transition: all`
- [ ] z-index uses fixed scale

## Reference Files

For detailed guidance on specific topics:

- [animations.md](animations.md) - Easing, timing, springs, performance
- [ui-polish.md](ui-polish.md) - Typography, shadows, gradients, scrollbars
- [forms-controls.md](forms-controls.md) - Inputs, buttons, form patterns
- [touch-accessibility.md](touch-accessibility.md) - Touch devices, keyboard nav, a11y
- [component-design.md](component-design.md) - Compound components, composition, props API
- [marketing.md](marketing.md) - Landing pages, blogs, docs
- [performance.md](performance.md) - Virtualization, preloading, optimization