# block-size

> Applies `block-size` — the logical height, which is the physical width in a vertical writing mode.

```ts
import { bs } from "@sdxc/u/size";
```

Applies `block-size` — the logical height, which is the physical width in
a vertical writing mode.

## Quick reference

Every documented call, beside the CSS it emits.

| Call | CSS |
| --- | --- |
| `u.bs("full")` | `css({ blockSize: "100%" })` |

## Examples

### Basic example

Use `bs(n)` with a step of the spacing scale, like `bs(16)` or `bs(32)`, to set an element's block size, its height in horizontal text:

```tsx
<div mix={[hstack({ gap: 4, align: "end" })]}>
	<div mix={[bs(12), is(20), ...]}>bs(12)</div>
	<div mix={[bs(20), is(20), ...]}>bs(20)</div>
	<div mix={[bs(28), is(20), ...]}>bs(28)</div>
	<div mix={[bs(36), is(20), ...]}>bs(36)</div>
	<div mix={[bs(44), is(20), ...]}>bs(44)</div>
</div>
```

### Filling the parent

Use `bs("full")` to fill the block size of a parent that sets one, or pass any CSS length as a string, like `bs("50%")`:

```tsx
<div mix={[hstack({ gap: 4, align: "start" }), bs(48), p(4), ...]}>
	<div mix={[bs("full"), is(28), ...]}>bs("full")</div>
	<div mix={[bs("50%"), is(28), ...]}>bs("50%")</div>
</div>
```

### Vertical writing modes

`bs()` sizes the block axis, so in a vertical writing mode like `vertical-rl` it sets the element's width instead of its height:

```tsx
<div mix={[...]}>
	<div mix={[bs(16), is(40), ...]}>horizontal-tb</div>
	<div mix={[bs(16), is(40), raw({ writingMode: "vertical-rl" }), ...]}>
		vertical-rl
	</div>
</div>
```

## Applying on a state

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

```ts
u.hover(u.bs("full"))
```

## Responsive design

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

```ts
u.at("md", u.bs("full"))
```

## 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
bs(4)
```

## Signature

```ts
u.bs(value: SizeValue)
```