Add a way to add custom css to the generated swagger html

I’m submitting a…

[ ] Regression 
[ ] Bug report
[x] Feature request
[ ] Documentation issue or request
[ ] Support request => Please do not submit support request here, instead post your question on Stack Overflow.

Current behavior

There’s no option to add custom styles to the generated swagger html

Expected behavior

have an option for the DocumentBuilder to setCustomCss that recieves a path to a css file (or scss file?)

Environment

Nest version: 5.0.0

 
For Tooling issues:
- Node version: 7.7.3
- Platform:  Mac

[kamilmysliwiec]

The SwaggerModule accepts options argument as a 4th argument:

public static setup(
    path: string,
    app: INestApplication,
    document: SwaggerDocument,
    options?: SwaggerCustomOptions
) {...}

These options are passed down to the underlying swagger-ui-express package. Here is a SwaggerCustomOptions interface:

export interface SwaggerCustomOptions {
  explorer?: boolean;
  swaggerOptions?: any;
  customCss?: string;
  customJs?: string;
  customfavIcon?: string;
  swaggerUrl?: string;
  customSiteTitle?: string;
}

as you see, there is a customCss property available already.

[kamilmysliwiec]

Maybe it is a good point to add it into the documentation 😃 feel free to create a PR, if you want to