Css function Composer type extends String type require length property is not needed

This problem is almost same as https://github.com/Temzasse/stitches-native/pull/26.
The css function needs same patch.
![スクリーンショット 2022-10-31 15 25 45](https://user-images.githubusercontent.com/7004725/198945473-4e13abd2-91c9-40f1-bf74-31d159863269.png)
