I think this is something which you should let your IDE handle. Most decent IDEs have code folding and quick search. Also keep in mind that many elements in y

I think this is something which you should let your IDE handle. Most decent IDEs have code folding and quick search. Also keep in mind that many elements in your website can have an average of 4-6 attributes. If you are using browser specific enhancements or hacks you can easily have more than 10 attributes for some of the elements. Now think about performing that dreaded horizontal scroll in your editor to find some of the attributes. Let the IDE take care of abstracting away the actual file structure. Let your build process take care of minifying the css files. Conventions are good in programming, but single-line css looks like a bit too extreme trade-off.