Preciso de um plugin codificado para permitir certas codificações CSS no fórum

[Kat_F]

This is what I was told:

@codinghorror

@Kat_F

Is it possible to create a theme that will allow users to use .css in posts without ruining security?

Not really? If you need a full CSS playground that suggests the use of something like codepen.com versus Discourse.