Changing "categories per row" for specific sub-categories only?

I have been led around in circles trying to figure this out for some time. We want some sub-categories to have 3 or 4 categories per row, and others to only have 1 (our default). For example:

Category A (all 1 category per row)

Sub-Category 1

Sub-Category I

Sub-Category II

Sub-Category III

Sub-Category 2

Sub-Category 3

Sub-Category 4

Category B (1 category per row)

Sub-Category 1 (1 category per row)

Sub-Category I (4 categories per row)

Sub-Category II (4 categories per row)

Sub-Category III (4 categories per row)

Sub-Category 2 (1 category per row)

Sub-Category I (4 categories per row)

Sub-Category II (4 categories per row)

Sub-Category III (4 categories per row)

Sub-Category 3

Sub-Category 4

From my understanding, this should be doable in CSS… that darn global setting for categories per row is throwing me off, though.

I should be able to create a new CSS file ("c_xx_xx.css" or "c_xx_xx_xx.css") to customize the layout of a specific sub-category. I am stuck from here, though. How do I specify in said CSS file the number of categories per row?

Thank you for any help you can provide!