# importCss

Emit an `@import` rule for an external stylesheet, with optional conditions.

`importCss` places the import at the top of the shared stylesheet, after the `@layer` order statement and before namespaces and ordinary rules. Repeated calls keep their authored order.

```ts title="src/imports.ts"
import { importCss } from 'zyzz/web'

// Imports the published file into the `reset` layer
importCss({ layer: 'reset', url: './normalize.css' })
```

## Signature

```ts
// One stylesheet with optional conditions
importCss(options)
```

## Parameters

### options.url

* **Type:** `string`

The stylesheet URL. A relative URL resolves against the declaring module, and the host publishes the file as an asset. Absolute URLs are emitted unchanged.

```ts
// Published as an asset, and the rule points at its URL
importCss({ url: './print.css' })
```

### options.layer

* **Type:** `string | true`
* **Default:** `undefined`

The cascade layer for the imported rules. `true` places them in an anonymous layer.

```ts
import { importCss } from 'zyzz/web'

// Emits `@import url("https://example.com/vendor.css") layer;`
importCss({ layer: true, url: 'https://example.com/vendor.css' })
```

### options.media

* **Type:** `string`
* **Default:** `undefined`

A media query list that conditions the import.

```ts
// Applies the imported rules only when printing
importCss({ media: 'print', url: './print.css' })
```

### options.supports

* **Type:** `string`
* **Default:** `undefined`

A supports condition or declaration, without the outer `supports()`.

```ts
import { importCss } from 'zyzz/web'

// Emits `@import url("https://example.com/grid.css") supports(display: grid);`
importCss({ supports: 'display: grid', url: 'https://example.com/grid.css' })
```

## Returns

`void`. The compiler erases the call and keeps the import in the shared stylesheet. Vite, Unplugin, and `zyzz/node` scan the source tree, so unimported modules still contribute. Next.js compiles only imported modules, so import the declaring module from an entrypoint there.

## Errors

TypeScript rejects unknown options and calls without `url`.

```ts
import { importCss } from 'zyzz/web'

// The option is `url`
importCss({ href: './reset.css' })
// error: Object literal may only specify known properties, and 'href' does not exist in type 'Options & Record<never, never>'.
```

The compiler reports `Source.ExtractError` for values it cannot read statically and calls outside module scope. Native builds reject the call with `Native.CompileError`.