UI Design Fundamentals

The definitive guide for building production-grade web interfaces. Covers the full stack of design decisions from layout to motion.

WHEN To Use

• Designing new UI components or pages
• Building landing pages, dashboards, or applications
• Reviewing code for design quality
• Creating distinctive interfaces that avoid generic aesthetics
• Implementing accessibility requirements

KEYWORDS

ui design, web design, layout, typography, color palette, spacing, visual hierarchy, responsive design, accessibility, motion design, component design, design tokens, frontend, css, tailwind

Design Philosophy

The 80/20 of Design Quality

Focus on typography and spacing first. They're 65% of perceived quality.

Commit to a Direction

Mediocrity is forgettable. Pick an extreme:

Layout

Grid vs Flexbox Decision

Container Strategy

/* Standard content width */
.container {
  width: 100%;
  max-width: 1280px;
  margin-inline: auto;
  padding-inline: clamp(1rem, 5vw, 3rem);
}

/* Full-bleed with contained content */
.full-bleed {
  width: 100vw;
  margin-left: calc(50% - 50vw);
}

Common Layout Mistakes

Typography

Typography carries 90% of a design's personality.

Font Pairing by Context

Type Scale (1.25 ratio)

--text-xs: 0.64rem;   /* 10px - captions */
--text-sm: 0.8rem;    /* 13px - secondary */
--text-base: 1rem;    /* 16px - body */
--text-lg: 1.25rem;   /* 20px - lead */
--text-xl: 1.563rem;  /* 25px - h4 */
--text-2xl: 1.953rem; /* 31px - h3 */
--text-3xl: 2.441rem; /* 39px - h2 */
--text-4xl: 3.052rem; /* 49px - h1 */

Typography Rules

Typography Mistakes

Color

Building a Palette

Every palette needs five functional roles:

Surface Layering (Dark Mode)

Create depth through lightness, not shadows:

:root {
  --surface-0: hsl(220 15% 8%);   /* page background */
  --surface-1: hsl(220 15% 12%);  /* card */
  --surface-2: hsl(220 15% 16%);  /* raised element */
  --surface-3: hsl(220 15% 20%);  /* popover/modal */
}

Contrast Requirements (WCAG)

Color Mistakes

Spacing

8px Base Unit Scale

--space-1: 0.25rem;  /* 4px - tight gaps */
--space-2: 0.5rem;   /* 8px - input padding */
--space-3: 0.75rem;  /* 12px - button padding */
--space-4: 1rem;     /* 16px - default spacing */
--space-6: 1.5rem;   /* 24px - section padding */
--space-8: 2rem;     /* 32px - section gaps */
--space-12: 3rem;    /* 48px - major breaks */
--space-16: 4rem;    /* 64px - page rhythm */

Spacing Rules

Spacing Mistakes

Visual Hierarchy

Guide the eye through deliberate contrast.

Hierarchy Techniques

Card Hierarchy Pattern

Eyebrow  ← xs, uppercase, muted color
Title    ← xl, semibold, primary color
Body     ← base, secondary color, 1.6 line-height
Action   ← spaced apart, mt-4 minimum

Responsive Design

Breakpoint Strategy

Fluid Techniques

/* Fluid typography */
h1 { font-size: clamp(2rem, 1.5rem + 2.5vw, 3.5rem); }

/* Fluid spacing */
section { padding-block: clamp(2rem, 1rem + 4vw, 6rem); }

/* Intrinsic grid */
.grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(min(100%, 20rem), 1fr));
  gap: var(--space-6);
}

Responsive Mistakes

Accessibility

Accessibility is not optional.

Critical Requirements

Focus Styles

:focus-visible {
  outline: 2px solid var(--color-primary);
  outline-offset: 2px;
}

/* Remove default only if custom exists */
:focus:not(:focus-visible) {
  outline: none;
}

Motion Safety

@media (prefers-reduced-motion: reduce) {
  *, *::before, *::after {
    animation-duration: 0.01ms !important;
    transition-duration: 0.01ms !important;
  }
}

Motion & Animation

Use motion to communicate, not decorate.

Timing Guidelines

Staggered Entrance

.item {
  opacity: 0;
  translate: 0 1rem;
  animation: reveal 0.5s ease-out forwards;
}
.item:nth-child(1) { animation-delay: 0ms; }
.item:nth-child(2) { animation-delay: 60ms; }
.item:nth-child(3) { animation-delay: 120ms; }

@keyframes reveal {
  to { opacity: 1; translate: 0 0; }
}

Motion Mistakes

Component States

Every interactive element needs clear states.

Button Example

.btn {
  transition: all 150ms ease-out;
}
.btn:hover {
  background: var(--color-primary-600);
}
.btn:active {
  transform: scale(0.98);
}
.btn:focus-visible {
  outline: 2px solid var(--color-primary);
  outline-offset: 2px;
}
.btn:disabled {
  opacity: 0.5;
  cursor: not-allowed;
}

Design Tokens Architecture

Structure tokens in three layers:

/* Layer 1: Primitives */
--blue-500: oklch(0.55 0.2 250);
--gray-100: oklch(0.95 0.005 250);
--radius-md: 0.5rem;

/* Layer 2: Semantic */
--color-primary: var(--blue-500);
--color-surface: var(--gray-100);
--radius-button: var(--radius-md);

/* Layer 3: Component */
--btn-bg: var(--color-primary);
--btn-radius: var(--radius-button);
--btn-padding: var(--space-2) var(--space-4);

This allows theme switching by remapping Layer 2 only.

Pre-Delivery Checklist

Typography

• [ ] Intentional font pairing (not system defaults)
• [ ] Consistent type scale
• [ ] Line length ≤ 75 characters
• [ ] 16px minimum body text

Color

• [ ] Cohesive palette (3-5 colors)
• [ ] WCAG contrast met (4.5:1 normal, 3:1 large)
• [ ] Semantic colors defined
• [ ] Dark mode tested (if applicable)

Spacing

• [ ] Consistent rhythm using scale
• [ ] No arbitrary pixel values
• [ ] Proper mobile padding

Hierarchy

• [ ] Clear visual flow
• [ ] Primary action obvious
• [ ] Information layered by importance

Responsive

• [ ] Mobile tested (375px)
• [ ] No horizontal overflow
• [ ] Touch targets ≥ 44px

Accessibility

• [ ] Keyboard navigable
• [ ] Focus visible
• [ ] Screen reader tested
• [ ] Motion-safe

States

• [ ] Hover on all interactive elements
• [ ] Focus-visible on all focusable
• [ ] Loading states for async
• [ ] Error states for forms

Performance

• [ ] Images optimized (WebP, srcset)
• [ ] Fonts subset
• [ ] Animations use transform/opacity

NEVER Do

1. NEVER skip contrast checking — Test every text/background combination
2. NEVER use color alone — Always pair with icons/text for meaning
3. NEVER remove focus outlines — Unless replacing with visible alternative
4. NEVER use arbitrary spacing — Stick to the scale
5. NEVER animate layout properties — Only transform and opacity
6. NEVER ignore reduced-motion — Always check the preference
7. NEVER center everything — Left-align body text
8. NEVER use tiny touch targets — 44px minimum
9. NEVER use low-contrast text — slate-600 minimum on white
10. NEVER use generic system fonts — Choose intentional typography

Related Skills

• ui-ux-pro-max — Searchable design databases with CLI
• frontend-design — Creative aesthetics, avoiding "AI slop"
• theme-factory — Applying themes to artifacts
• design-system-patterns — Token architecture and theming