# backdropContrast

> Pushes the backdrop away from (above `1`) or toward (below `1`) mid-grey; flattening it to a uniform tone keeps overlaid text legible.

```ts
import { backdropContrast } from "@sdxc/u/effects";
```

Pushes the backdrop away from (above `1`) or toward (below `1`) mid-grey;
flattening it to a uniform tone keeps overlaid text legible. Needs a partly
transparent host; sibling utilities combine; `u.transparencySafe()` gates it.

## Quick reference

Every documented call, beside the CSS it emits.

| Call | CSS |
| --- | --- |
| `u.backdropContrast()` | `css({ "--ui-backdrop-contrast": "1.25", backdropFilter: "... contrast(var(--ui-backdrop-contrast, 1)) ...", WebkitBackdropFilter: "... contrast(var(--ui-backdrop-contrast, 1)) ..." })` |
| `u.transparencySafe(u.backdropContrast(0.75))` | `css({ "@media (prefers-reduced-transparency: no-preference)": { "--ui-backdrop-contrast": "0.75", backdropFilter: "...", WebkitBackdropFilter: "..." } })` |

## Examples

### Basic example

Use `backdropContrast(n)` to flatten what shows through an element toward grey below `1`, or push it apart above `1`:

```tsx
<div mix={[...]}>
	<div mix={[...]}>
		<div mix={[backdropContrast(0.4), ...]}>backdropContrast(0.4)</div>
	</div>
	<div mix={[...]}>
		<div mix={[backdropContrast(2), ...]}>backdropContrast(2)</div>
	</div>
</div>
```

## Applying on a state

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

```ts
u.hover(u.backdropContrast())
```

## Responsive design

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

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

## Signature

```ts
u.backdropContrast(value?: number | (string & {}))
```