Some CSS errors are not detected if they are at the start of the file, but detected when they are in the middle (?)

Example:

This generates no errors:
```css
}

.garden-link::before {
content: "🦚"
}
```

This generates an error:
```css
.garden-link::before {
content: "🦚"
}

}
```

More generally I seem to be able to put semi-arbitrary things at the start of the file...