Are you working with K2 component ? you need each category of K2 has seperate style, K2 not support class suffix for Category,so you don't know how to solve it. Now, It is simple with Jms K2 category class plugin, install it and config class suffix for k2 category following Category ID
Class Type : Class type to add , It supports 2 options : New Class (example : "ItemListView red") and Class suffix (example : "ItemListView_red").
Categories Class Define : Define class for each category, syntax for it :
[Category ID]:[Class Name Or Class Suffix Name]
Each category per a line, example :