# CSS loading

The `css-load` extension checks that a client requests a CSS resource from BotStopper. The challenge page imports a test route. BotStopper checks that the client requests that route before it accepts the challenge.

## Configuration

Add `css-load` to the `extensions` list in an existing challenge definition:

```yaml
thresholds:
  - name: mild-suspicion
    expression:
      all:
        - weight > 0
        - weight < 10
    action: CHALLENGE
    challenge:
      algorithm: fast
      difficulty: 2
      report_as: 2
      extensions:
        - css-load
```

This example adds the extension to the [fast challenge](/docs/challenges/fast.md). Refer to [thresholds](/docs/configuration/thresholds.md) for challenge selection and [expressions](/docs/configuration/expressions.md) for expression syntax.