# flex-basis

> Applies `flex-basis`, defaulting to `"auto"` to match the property's own initial value — the remainder of a `flex: N N M` shorthand once `u.grow()`/`u.shrink()` have been extracted from it.

```ts
import { basis } from "@sdxc/u/layout";
```

Applies `flex-basis`, defaulting to `"auto"` to match the property's own
initial value — the remainder of a `flex: N N M` shorthand once
`u.grow()`/`u.shrink()` have been extracted from it.

## Quick reference

Every documented call, beside the CSS it emits.

| Call | CSS |
| --- | --- |
| `u.basis()` | `css({ flexBasis: "auto" })` |
| `u.basis("0%")` | `css({ flexBasis: "0%" })` |
| `u.basis(4)` | `css({ flexBasis: "calc(var(--ui-spacing, 0.25rem) * 4)" })` |

## Examples

### Basic example

Use `basis(n)` with a step of the spacing scale, like `basis(32)` or `basis(64)`, to set the size a flex item starts from:

```tsx
<div mix={[flex(), gap(4)]}>
	<div mix={[basis(32), ...]}>basis(32)</div>
	<div mix={[basis(32), ...]}>basis(32)</div>
	<div mix={[basis(64), ...]}>basis(64)</div>
</div>
```

### Using a percentage

Pass a percentage like `basis("25%")` to size an item as a share of its container:

```tsx
<div mix={[flex(), gap(4)]}>
	<div mix={[basis("25%"), ...]}>25%</div>
	<div mix={[basis("25%"), ...]}>25%</div>
	<div mix={[basis("50%"), ...]}>basis("50%")</div>
</div>
```

### Starting from zero

With `basis()` items grow from their content size; with `basis("0%")` they grow from nothing, so `grow()` splits the row into equal parts:

```tsx
<div mix={[...]}>
	<div mix={[flex(), gap(4)]}>
		<div mix={[grow(), basis(), ...]}>basis()</div>
		<div mix={[grow(), basis(), ...]}>a long label</div>
		<div mix={[grow(), basis(), ...]}>short</div>
	</div>
	<div mix={[flex(), gap(4)]}>
		<div mix={[grow(), basis("0%"), ...]}>basis("0%")</div>
		<div mix={[grow(), basis("0%"), ...]}>a long label</div>
		<div mix={[grow(), basis("0%"), ...]}>short</div>
	</div>
</div>
```

## Applying on a state

Wrap the call in a state utility to scope it to one selector.

```ts
u.hover(u.basis())
```

## Responsive design

Wrap the call in a container query to scope it to one width.

```ts
u.at("md", u.basis())
```

## Customizing your theme

### Customizing spacing

Every numeric step multiplies `--ui-spacing`, so redefining it rescales every spacing and sizing utility at once:

```css
:root {
	--ui-spacing: 0.25rem;
}
```

Every call that names the step now reads the new value:

```ts
basis(4)
```

## Signature

```ts
u.basis(value?: SizeValue)
```