In CSS there is no concept of sections or nested blocks. But since CSS files usually become very long, you may want to fold groups of style definitions to get a better overview:

/* start foldme */
p { color: #000 }
/* end foldme */

Since this is not possible with the CSS bundle shiped with Textmate, I added this on myself:

1. I first added a snipped called section to the CSS bundle:

   /* start ${1:section} */
   $0
   /* end $1 */
   

   It gets activated by the tab trigger sec. The scope selector is source.css.

2. I then modified the language definition and added |/\* start \w+ \*/ to the foldingStartMarker and |/\* end \w+ \*/ to the foldingStopMarker. They should look like this now:

   foldingStartMarker = '/\*\*(?!\*)|\{\s*($|/\*(?!.*?\*/.*\S))|/\* start \w+ \*/';
   foldingStopMarker = '(?<!\*)\*\*/|^\s*\}|/\* end \w+ \*/';
   

That’s all you need to do.