use Views module with organic group Using Views, I was able to apply CSS elements to content fields, but after applying Organic Group module and assigning each content to each group, I don't know how to take control of these content. The contents looks fine in the front page but inside the group's page it is a bit messy.

So is there's any way to fix that?
This module Code Per Node will make things alot easier for you.

Code per Node makes it possible to add custom CSS and Javascript per node, per content type, per block, and globally. The code is stored in the database, but served from the file system. It also supports syntax highlighting with CodeMirror.