## Migrate twenty-ui from Emotion to Linaria
Completes the migration of all `twenty-ui` components from Emotion
(runtime CSS-in-JS) to Linaria (zero-runtime, CSS extracted at build
time).
- Replaced `@emotion/styled` with `@linaria/react` across ~170 files
- Removed all Emotion dependencies from `twenty-ui`
- Introduced a CSS custom properties-based theme system:
`themeCssVariables` where every leaf is a `var(--t-xxx)` reference,
injected onto `document.documentElement` by
`ThemeCssVariableInjectorEffect`
- No more `theme` prop threading — styled components reference
`themeCssVariables.x.y` directly at build time
- Updated `twenty-front` consumers to remove `theme={theme}` prop
passing
**Before / After:**
```tsx
// Emotion
color: ${({ theme }) => theme.font.color.primary};
padding: ${({ theme }) => theme.spacing(4)};
// Linaria
color: ${themeCssVariables.font.color.primary};
padding: ${themeCssVariables.spacing[4]};
```
### Theme architecture
Two build-time utilities produce the theme system:
- **`buildThemeReferencingRootCssVariables`** — walks the theme object
and builds a nested mirror where every leaf is a `var(--t-xxx)` string
(evaluated at build time by wyw-in-js)
- **`prepareThemeForRootCssVariableInjection`** — walks the runtime
theme and collects flat `[--css-variable-name, value]` pairs, injected
onto `document.documentElement` by `ThemeCssVariableInjectorEffect`
Both share naming conventions (`camelToKebab`, `SPACING_VALUES`,
`formatSpacingKey`) and are unit tested.
### Spacing cleanup
Spacing scale now uses integers 0–32 (generated via loop), with `0.5`
and `1.5` as the only fractional exceptions. All other fractional
spacing usages (`0.25`, `0.75`, `1.25`, `2.5`, `3.5`) were replaced with
literal pixel values across ~20 twenty-front files.
### Framer Motion integration
Linaria doesn't support `styled(motion.div)` — wrapping a motion element
with `styled()` causes the component body to be stripped at build time.
Instead, we define the styled component first, then wrap it with
`motion.create()`:
```tsx
const StyledBarBase = styled.div`
background-color: ${themeCssVariables.font.color.primary};
height: 100%;
`;
const StyledBar = motion.create(StyledBarBase);
```
### Block interpolations
Linaria doesn't support interpolations that return multiple CSS
declarations (Linaria wraps the entire block in a single `var()`,
producing invalid CSS). These were split into individual property
interpolations:
```tsx
// Emotion — single interpolation returning multiple declarations
border-left: ${({ divider, theme }) => {
const border = `1px solid ${theme.border.color.light}`;
return divider ? `border-${divider}: ${border}` : '';
}}
// Linaria — one interpolation per property
border-left: ${({ divider }) =>
divider === 'left' ? `1px solid ${themeCssVariables.border.color.light}` : 'none'};
border-right: ${({ divider }) =>
divider === 'right' ? `1px solid ${themeCssVariables.border.color.light}` : 'none'};
```
### Dynamic styles via CSS variables
When a component needs to compute styles from multiple props with
complex branching logic (e.g. `Button` combining `variant`, `accent`,
`inverted`, `disabled`, `focus`, `position`), Linaria's prop
interpolations become unwieldy. In those cases we use a
`computeDynamicStyles` function that returns a `CSSProperties` object
injected via `style={}`, referenced from the static CSS with `var()`:
```tsx
const StyledButton = styled.button`
background: var(--btn-bg);
border-color: var(--btn-border-color);
&:hover { background: var(--btn-hover-bg); }
`;
const dynamicStyles = useMemo(() => {
const s = computeButtonDynamicStyles(variant, accent, ...);
return { '--btn-bg': s.background, '--btn-hover-bg': s.hoverBackground } as CSSProperties;
}, [variant, accent, ...]);
return <StyledButton style={dynamicStyles} />;
```
### CSS var + unit concatenation
CSS custom properties can't be concatenated with unit suffixes directly
(`var(--x)px` is invalid). Values that need units use `calc()`:
```tsx
// Broken
transition: background ${themeCssVariables.animation.duration.instant}s ease;
// Fixed
transition: background calc(${themeCssVariables.animation.duration.instant} * 1s) ease;
```
