Agent Skills: StyleX Styling

StyleX Styling

This project uses StyleX for all styling. The system has three layers: design tokens for values, design primitives for multi-property patterns, and stylex.create for component-specific styles. All styles are applied via a custom css prop.

Quick Decision Guide

| Need | Use | Example | | ------------------------------------------------------ | ----------------------------- | ----------------------------------------------- | | Flex layout, fills, truncation, resets, transitions | Design primitives | css={flex.row} | | Override a primitive's default | Layout modifier | css={[flex.row, align.end]} | | Single-property styling (color, spacing, font, border) | stylex.create + tokens | color: color.textMain | | Responsive behavior | stylex.create + breakpoints | { default: "none", [breakpoints.md]: "flex" } | | Pseudo-selectors (hover, focus) | stylex.create | { default: val, ":hover": hoverVal } |

Custom css Prop

Use css={styles.foo} instead of {...stylex.props(styles.foo)}. This is transpiled by a custom Babel plugin.

// Single style
<div css={styles.card}>

// Composed — array of styles, primitives, and conditionals
<div css={[flex.row, styles.header, isActive && styles.active]}>

Design Tokens

Import from #src/tokens.stylex.ts. All tokens are theme-aware. For the full catalog of every token and its values, read references/tokens.md.

Categories: color, space, controlSize, font, border, shadow, layer, ratio.

import { color, space, border, font } from "#src/tokens.stylex.ts";

const styles = stylex.create({
  card: {
    padding: space._4,
    borderRadius: border.radius_3,
    backgroundColor: color.backgroundRaised,
    fontSize: font.uiBody,
  },
});

Breakpoints

Import from #src/breakpoints.stylex.ts. Values: sm (320px), md (768px), lg (1080px), xl (2000px).

import { breakpoints } from "#src/breakpoints.stylex.ts";

const styles = stylex.create({
  grid: {
    display: { default: "none", [breakpoints.md]: "grid" },
    gridTemplateColumns: { default: "1fr", [breakpoints.lg]: "repeat(3, 1fr)" },
  },
});

Design Primitives

Composable multi-property styles in src/primitives/. Each primitive bundles 2+ CSS properties that encode a common pattern. For full API tables, read references/primitives.md.

Flex (#src/primitives/flex.stylex.ts)

The most commonly used primitives. Flex patterns set display: flex plus layout defaults:

• flex.row — horizontal, vertically centered
• flex.col — vertical stack
• flex.center — centered both axes
• flex.between — space-between with vertical centering
• flex.wrap — wrapping row
• flex.inlineCenter — inline-flex centered

Override defaults with modifiers: align.{start,center,end,baseline,stretch}, justify.{start,center,end,between}, grow.{_0,_1}, shrink.{_0,_1}.

import { flex, align, justify } from "#src/primitives/flex.stylex.ts";

<div css={flex.row}>                        {/* basic row */}
<div css={[flex.row, align.end]}>           {/* row, bottom-aligned */}
<header css={flex.between}>                 {/* toolbar pattern */}
<div css={[flex.col, justify.center]}>      {/* vertically centered column */}

Other Primitives (see references/primitives.md)

• Layout — position fills, scroll containers, truncation, image fit
• Reset — buttonReset.base strips browser button chrome
• Motion — transition/animation presets with reduced-motion handling

Best Practices

1. Primitives for multi-property patterns — flex, fills, truncation, resets, transitions
2. Tokens for single properties — fontSize: font.uiBody, gap: space._3
3. Always use the css prop — never {...stylex.props()}
4. Conditional styles via arrays — css={[base, condition && conditional]}
5. Mobile-first — use breakpoint overrides for larger screens
6. Theme-aware colors — use color tokens that adapt to light/dark
7. Logical properties — prefer paddingBlock/paddingInline over directional
8. Pseudo-selectors as object keys — { default: val, ":hover": hoverVal }