Ngx-formly: Defining CSS Class on Formly Material Radio

[Carbammato]

I'm submitting a ...

[ ] bug report => search github for a similar issue or PR before submitting
[ ] feature request
[X] support request

Current behavior
Hello everyone. As I'm trying to create a formly with some design from Material, I got some problems with the Radio button (type: button). Basically, I'd like to have a list of options aligned in vertical (and not inline), but the closest I can get, is a list of four option, 2 of them in the first row, the other 2 on the second row. I've an example in a Stackblitz attached.

Also, is there a chance to get to add some margin, or some spacing, between an option and the next one on the same line? It would improve readibility a lot.

Expected behavior
More or less, what I can get from the bootstrap example of a radio button (https://formly.dev/ui/bootstrap), but with some Material Design (https://material.angular.io/components/radio/examples , like the mat-radio example given)

Minimal reproduction of the problem with instructions
Here is a Stackblitz link:
https://stackblitz.com/edit/formly-css-pg
I loaded bootstrap via link on Index.html page, and added _d-inline-flex flex-column_ classes, but the result is quite odd.

What is the motivation / use case for changing the behavior?

Please tell us about your environment:

• Angular version: 6.0.X

• ngx-formly version: 4.2.X
  ...and basically what you can see from the stackblitz
  

• Browser: Chrome 67.0.3396.62
  _(I admit I only tried on Chrome)_
  

Thank you for any kind of help you may give me, as well for the effort you're doing.

[aitboudad]

you can use custom style like in material example, see https://stackblitz.com/edit/formly-css-pg-zbh3s6?file=src/styles.scss