# margin-block-start

> Applies `margin-block-start` — the leading block edge, the top edge in a horizontal writing mode.

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

Applies `margin-block-start` — the leading block edge, the top edge in a
horizontal writing mode.

## Quick reference

Every documented call, beside the CSS it emits.

| Call | CSS |
| --- | --- |
| `u.mbs(4)` | `css({ marginBlockStart: "calc(var(--ui-spacing, 0.25rem) * 4)" })` |

## Examples

### Basic example

Use `mbs(n)` to add margin to the block-start edge of an element, above it in horizontal text:

```tsx
<div mix={[...]}>
	<div mix={[mbs(8), ...]}>mbs(8)</div>
</div>
```

## Using a custom value

Every scale argument also takes a raw CSS value, which passes through untouched.

```ts
u.mbs("2.75rem")
```

## Applying on a state

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

```ts
u.hover(u.mbs(4))
```

## Responsive design

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

```ts
u.at("md", u.mbs(4))
```

## 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
mbs(4)
```

## Signature

```ts
u.mbs(value: SpacingValue)
```