mmb L

**Note**: This is not exactly a continuation of https://github.com/StylishThemes/GitHub-Dark/pull/568. I just mostly used coloring rules from the Twilight Theme which looks the most consistent and replaced the colors with Material...

## Description Currently, if a model is defined as ``` class Hero(GraphQLQueryBaseModel): name: str friends: List[str] ``` calling `graphql_fields` crashes with ``` AttributeError: type object 'str' has no attribute 'model_fields'...