# rotateY

> Rotates the element in 3D around its vertical axis — a flip-card or page-turn effect.

```ts
import { rotateY } from "@sdxc/u/transform";
```

Rotates the element in 3D around its vertical axis — a flip-card or
page-turn effect. Pair with `u.backfaceVisibility()` to hide the reversed
face mid-rotation. Composable with every other `transform/` utility.

## Quick reference

Every documented call, beside the CSS it emits.

| Call | CSS |
| --- | --- |
| `u.rotateY(180)` | `css({ "--ui-rotate-y": "180deg", transform: "... rotateY(var(--ui-rotate-y, 0deg)) ..." })` |

## Examples

### Basic example

Use `rotateY(n)` with a number of degrees to swing an element around its vertical axis, and `perspective()` on the parent to give it depth:

```tsx
<div mix={[...]}>
	<div mix={[perspective(400), ...]}>
		<div mix={[rotateY(30), ...]}>rotateY(30)</div>
	</div>
	<div mix={[perspective(400), ...]}>
		<div mix={[rotateY(50), ...]}>rotateY(50)</div>
	</div>
	<div mix={[perspective(400), ...]}>
		<div mix={[rotateY(-50), ...]}>rotateY(-50)</div>
	</div>
</div>
```

### Combining rotations

Every transform utility composes, so `rotateY()`, `rotateX()` and `rotate()` on one element apply together:

```tsx
<div mix={[...]}>
	<div mix={[perspective(400), ...]}>
		<div mix={[rotateY(40), rotateX(20), ...]}>rotateY + rotateX</div>
	</div>
	<div mix={[perspective(400), ...]}>
		<div mix={[rotateY(-40), rotate(10), ...]}>rotateY + rotate</div>
	</div>
</div>
```

### Showing the back face

A `rotateY(180)` turns the element to show its mirrored back; add `backfaceVisibility()` to hide it, as a flip card does:

```tsx
<div mix={[...]}>
	<div mix={[perspective(400), ...]}>
		<div mix={[rotateY(180), ...]}>rotateY(180)</div>
	</div>
	<div mix={[perspective(400), ...]}>
		<div mix={[rotateY(180), backfaceVisibility(), ...]}>hidden</div>
	</div>
</div>
```

## Using a custom value

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

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

## Applying on a state

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

```ts
u.hover(u.rotateY(180))
```

## Responsive design

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

```ts
u.at("md", u.rotateY(180))
```

## Signature

```ts
u.rotateY(value: AngleValue)
```