What is that? Where did you get this file and what are you asking about, actually?
bbs_default_style.ccs is part of the files for minibb. I downloaded miniBB.zip from http://www.minibb.com/download.html.
I extracted the files to a folder called forum. In forum is directory is bbs_default_style.ccs.
MiniBB uses bbs_default_style.ccs to display the style sheets for its presentation of its documents. Each browser uses the bbs_default_style.ccs to display its presentation of MiniBB. However the Firefox browser cannot display bbs_default_style.ccs and therefore renders the HTML without color or formatting.