Styling & Theming

This page covers comprehensive styling standards for Decentraland web UIs using styled-components with Material UI's styling solution.

Core Principles

1. Object syntax only - Use object notation for strong TypeScript support
2. Theme-first - All values come from the UI2 theme
3. No inline styles - Use styled components for all styling
4. Typed everything - Leverage TypeScript for props and theme
5. Responsive by default - Use theme breakpoints

---

Object Syntax Standard

UI2 components MUST use the object syntax. This ensures strong TypeScript support, csstype validation, and direct theme integration.

Basic Example

// ✅ Good: Object syntax
const Button = styled('button')({
  color: 'turquoise',
  padding: '8px 16px',
});

// ❌ Bad: Template literal syntax
const Button = styled.button`
  color: turquoise;
  padding: 8px 16px;
`;

With Theme and Props

interface ButtonProps {
  primary?: boolean;
  size?: 'small' | 'medium' | 'large';
}

// ✅ Good: Object syntax with theme and props
const Button = styled('button')<ButtonProps>(({ theme, primary, size = 'medium' }) => ({
  color: primary ? theme.palette.primary.main : theme.palette.text.primary,
  backgroundColor: primary ? theme.palette.primary.main : 'transparent',
  borderRadius: theme.shape.borderRadius,
  padding: {
    small: theme.spacing(0.5, 1),
    medium: theme.spacing(1, 2),
    large: theme.spacing(1.5, 3),
  }[size],
}));

---

Element Syntax

When styling native HTML elements, always use the function call form styled('tag').

Correct Syntax

// ✅ Good: Function call form
const Container = styled('div')({
  display: 'flex',
  flexDirection: 'column',
});

const Action = styled('button')(({ theme }) => ({
  color: theme.palette.primary.main,
  padding: theme.spacing(1, 2),
}));

const Label = styled('label')(({ theme }) => ({
  color: theme.palette.text.secondary,
  fontSize: theme.typography.caption.fontSize,
}));

Incorrect Syntax

// ❌ Bad: Property form (legacy syntax)
const Container = styled.div`
  display: flex;
  flex-direction: column;
`;

const Action = styled.button`
  color: ${props => props.theme.palette.primary.main};
`;

---

No Inline Styles

Inline styles (style={...}) MUST NOT be used in UI2 components.

Why Not Inline Styles?

• Bypass theme typing
• Harder to maintain
• Prevent reusability
• Can't be optimized
• No TypeScript validation

The Right Way

// ❌ Bad: Inline styles
<Card 
  key={id} 
  style={{ backgroundColor: color } as React.CSSProperties}
>
  <CardHeader>
    <Title style={{ fontSize: 20 }}>{title}</Title>
  </CardHeader>
</Card>

// ✅ Good: Styled components with props
interface CardProps {
  backgroundColor: string;
}

interface TitleProps {
  size: number;
}

const StyledCard = styled('div')<CardProps>(({ backgroundColor, theme }) => ({
  backgroundColor,
  borderRadius: theme.shape.borderRadius,
  padding: theme.spacing(2),
}));

const Title = styled('h2')<TitleProps>(({ size, theme }) => ({
  fontSize: theme.typography.pxToRem(size),
  color: theme.palette.text.primary,
}));

<StyledCard key={id} backgroundColor={color}>
  <CardHeader>
    <Title size={20}>{title}</Title>
  </CardHeader>
</StyledCard>

---

Breakpoints

Use theme.breakpoints helpers instead of hardcoded pixel values.

Breakpoint Helpers

Helper	Usage	Description
up(key)	theme.breakpoints.up('md')	Min-width and up
down(key)	theme.breakpoints.down('md')	Max-width and down
between(start, end)	theme.breakpoints.between('sm', 'lg')	Between two breakpoints
only(key)	theme.breakpoints.only('md')	Only at this breakpoint

Examples

// ❌ Bad: Hardcoded breakpoints
const Panel = styled('div')`
  @media (max-width: 768px) {
    width: 100%;
  }
`;

// ✅ Good: Theme breakpoints
interface PanelProps {
  expanded: boolean;
}

const Panel = styled('div')<PanelProps>(({ theme, expanded }) => ({
  width: expanded ? '400px' : '0',
  transition: theme.transitions.create('width'),
  
  [theme.breakpoints.down('sm')]: {
    width: expanded ? '100%' : '0',
  },
}));

Multiple Breakpoints

const Layout = styled('div')(({ theme }) => ({
  display: 'grid',
  gridTemplateColumns: '1fr 320px',
  gap: theme.spacing(2),
  
  // Mobile: single column
  [theme.breakpoints.down('md')]: {
    gridTemplateColumns: '1fr',
  },
  
  // Large desktop: wider sidebar
  [theme.breakpoints.up('xl')]: {
    gridTemplateColumns: '1fr 400px',
  },
  
  // Tablet range: different gap
  [theme.breakpoints.between('sm', 'lg')]: {
    gap: theme.spacing(3),
  },
  
  // Only tablet
  [theme.breakpoints.only('md')]: {
    padding: theme.spacing(2),
  },
}));

---

Spacing Scale

Use theme.spacing exclusively for margins, paddings, and gaps.

Spacing Convention

• theme.spacing(n) where n is a number
• Base unit is typically 8px
• spacing(1) = 8px, spacing(2) = 16px, etc.
• Decimals allowed: spacing(1.5) = 12px

// ✅ Good: Theme spacing
const Box = styled('div')(({ theme }) => ({
  padding: theme.spacing(2),           // 16px
  margin: theme.spacing(1, 0),         // 8px vertical, 0 horizontal
  gap: theme.spacing(1.5),             // 12px
  paddingInline: theme.spacing(3),     // 24px left/right
}));

// ❌ Bad: Raw pixel values
const Box = styled('div')({
  padding: '16px',
  margin: '8px 0',
  gap: '12px',
});

Common Spacing Patterns

const Card = styled('div')(({ theme }) => ({
  // Even spacing all around
  padding: theme.spacing(3),
  
  // Different vertical/horizontal
  padding: theme.spacing(2, 3),  // 16px vertical, 24px horizontal
  
  // All sides different
  padding: theme.spacing(1, 2, 3, 2),  // top, right, bottom, left
  
  // Logical properties (preferred for RTL support)
  paddingBlock: theme.spacing(2),      // top and bottom
  paddingInline: theme.spacing(3),     // left and right
  marginBlockStart: theme.spacing(1),  // margin-top
}));

---

Z-Index and Stacking

Follow the theme's z-index scale. Never use arbitrary z-index values.

Theme Z-Index Values

theme.zIndex.mobileStepper  // 1000
theme.zIndex.fab            // 1050
theme.zIndex.speedDial      // 1050
theme.zIndex.appBar         // 1100
theme.zIndex.drawer         // 1200
theme.zIndex.modal          // 1300
theme.zIndex.snackbar       // 1400
theme.zIndex.tooltip        // 1500

Correct Usage

// ✅ Good: Theme z-index
const StickyBar = styled('div')(({ theme }) => ({
  position: 'sticky',
  top: 0,
  zIndex: theme.zIndex.appBar,
  backgroundColor: theme.palette.background.paper,
}));

const Overlay = styled('div')(({ theme }) => ({
  position: 'fixed',
  inset: 0,
  zIndex: theme.zIndex.modal,
  backgroundColor: 'rgba(0, 0, 0, 0.5)',
}));

// ❌ Bad: Arbitrary z-index
const StickyBar = styled('div')({
  position: 'sticky',
  top: 0,
  zIndex: 999,  // Don't do this
});

Stacking Context Best Practices

• Be conscious of creating new stacking contexts
• Avoid unnecessary position: relative on parents
• Document why a z-index is needed
• If you need a new layer, add it to the theme first

---

Color Tokens

Always consume colors from theme.palette and dclColors. No ad-hoc hex values.

Palette Structure

// Text colors
theme.palette.text.primary
theme.palette.text.secondary
theme.palette.text.disabled

// Background colors
theme.palette.background.default
theme.palette.background.paper

// Primary/Secondary/Error
theme.palette.primary.main
theme.palette.primary.light
theme.palette.primary.dark
theme.palette.primary.contrastText

// Action colors
theme.palette.action.active
theme.palette.action.hover
theme.palette.action.selected
theme.palette.action.disabled
theme.palette.action.disabledBackground

// Dividers
theme.palette.divider

Decentraland Colors

import { dclColors } from 'decentraland-ui2';

// Rarity colors
dclColors.rarity.unique
dclColors.rarity.mythic
dclColors.rarity.legendary
dclColors.rarity.epic
dclColors.rarity.rare
dclColors.rarity.uncommon
dclColors.rarity.common

Examples

// ✅ Good: Theme colors
const Chip = styled('span')(({ theme }) => ({
  color: theme.palette.text.secondary,
  backgroundColor: theme.palette.background.paper,
  borderColor: theme.palette.divider,
  
  '&:hover': {
    backgroundColor: theme.palette.action.hover,
  },
}));

const RarityBadge = styled('span')<{ rarity: string }>(({ rarity }) => ({
  backgroundColor: dclColors.rarity[rarity],
  color: '#FFFFFF', // Contrast color - acceptable if documented
  padding: '4px 8px',
  borderRadius: '4px',
}));

// ❌ Bad: Arbitrary hex values
const Chip = styled('span')({
  color: '#666666',
  backgroundColor: '#FFFFFF',
  borderColor: '#E0E0E0',
});

---

Interactive States

All interactive controls MUST show visible states for hover, focus, active, and disabled.

Complete Interactive Component

const InteractiveButton = styled('button')(({ theme }) => ({
  // Base state
  padding: theme.spacing(1, 2),
  backgroundColor: theme.palette.primary.main,
  color: theme.palette.primary.contrastText,
  border: 'none',
  borderRadius: theme.shape.borderRadius,
  cursor: 'pointer',
  outline: 'none',
  transition: theme.transitions.create([
    'background-color',
    'transform',
    'box-shadow',
  ]),
  
  // Hover state (mouse)
  '&:hover': {
    backgroundColor: theme.palette.primary.dark,
  },
  
  // Focus state (keyboard navigation)
  '&:focus-visible': {
    outline: `2px solid ${theme.palette.primary.main}`,
    outlineOffset: 2,
    boxShadow: theme.shadows[2],
  },
  
  // Active/Pressed state
  '&:active': {
    backgroundColor: theme.palette.primary.dark,
    transform: 'scale(0.98)',
  },
  
  // Disabled state
  '&:disabled': {
    backgroundColor: theme.palette.action.disabledBackground,
    color: theme.palette.action.disabled,
    cursor: 'not-allowed',
    transform: 'none',
  },
}));

Focus-Visible Pattern

Always use :focus-visible instead of :focus to avoid showing focus rings on mouse clicks:

// ✅ Good: Only shows focus ring for keyboard
'&:focus-visible': {
  outline: `2px solid ${theme.palette.primary.main}`,
  outlineOffset: 2,
}

// ❌ Bad: Shows focus ring on every click
'&:focus': {
  outline: `2px solid ${theme.palette.primary.main}`,
}

---

Typography

Use theme typography variants instead of custom font properties.

// ✅ Good: Typography variants
const Heading = styled('h1')(({ theme }) => ({
  ...theme.typography.h1,
  marginBottom: theme.spacing(2),
}));

const Body = styled('p')(({ theme}) => ({
  ...theme.typography.body1,
  color: theme.palette.text.secondary,
}));

// With MUI Typography component (preferred)
<Typography variant="h1">Heading</Typography>
<Typography variant="body1">Body text</Typography>

// ❌ Bad: Custom typography
const Heading = styled('h1')({
  fontSize: '32px',
  fontWeight: 700,
  lineHeight: 1.2,
});

---

Performance Optimization

Don't Create Styled Components in Render

// ❌ Bad: Creates new component on every render
function Component({ color }) {
  const Box = styled('div')({
    backgroundColor: color,
  });
  return <Box />;
}

// ✅ Good: Create once, pass props
const Box = styled('div')<{ color: string }>(({ color }) => ({
  backgroundColor: color,
}));

function Component({ color }) {
  return <Box color={color} />;
}

Memoize Derived Props

// ❌ Bad: Creates new object on every render
<StyledComponent style={{ color: isDark ? 'white' : 'black' }} />

// ✅ Good: Pass primitive props
const StyledComponent = styled('div')<{ isDark: boolean }>(({ isDark, theme }) => ({
  color: isDark ? theme.palette.common.white : theme.palette.common.black,
}));

<StyledComponent isDark={isDark} />

---

Naming Conventions

Component Names

• PascalCase for components
• Descriptive names

// ✅ Good names
const UserCard = styled('div')({...});
const PrimaryButton = styled('button')({...});
const NavigationList = styled('ul')({...});

// ❌ Bad names
const card = styled('div')({...});
const btn = styled('button')({...});
const list1 = styled('ul')({...});

File Structure

Component.tsx        # Main component
Component.styles.ts  # Styled components
Component.test.tsx   # Tests
Component.stories.tsx # Storybook

---

Next Steps

• Review Custom Components for component creation guidelines
• See Migration Guide for UI1 to UI2 migrations
• Check Process Overview for the complete workflow