Prevents [theme app extensions](/docs/apps/build/online-store/theme-app-extensions) from using CSS files larger than the configured [`threshold_in_bytes`](#options). Limiting the size of CSS files helps to improve the performance of your theme app extension.

## Example

In the following example, the size of `assets/app.css` is checked to make sure that it doesn't exceed the specified `threshold_in_bytes`:



```liquid
{% schema %}
{
  ...
  "stylesheet": "app.css"
}
{% endschema %}
```



## Options

The following example contains the default configuration for this check:

```yaml
AssetSizeAppBlockCss:
  enabled: true
  severity: suggestion
  threshold_in_bytes: 100_000
```

| Parameter | Description |
| --- | --- |
| `enabled` | Whether this check is enabled. |
| `severity` | The [severity](/docs/storefronts/themes/tools/theme-check/configuration#check-severity) of the check. |
| `threshold_in_bytes` | The maximum allowed compressed size, in bytes, for a single CSS file. Reflects the [suggested limit](/docs/apps/build/online-store/theme-app-extensions/configuration#file-and-content-size-limits) for theme app extension CSS, and includes theme and remote stylesheets. |

## Disabling this check

This check is enabled by default when you run the Shopify CLI 3.x [`build`](/docs/api/shopify-cli/app/app-build) command on an app that contains a theme app extension. This limit is not yet enforced, but disabling this check isn't recommended for theme app extensions.

This check is disabled by default when you run the Shopify CLI 2.x [`shopify theme check`](/docs/storefronts/themes/tools/theme-check/commands) command.