This is a very good question
Css is central superior service, now also known as competitive exam (c.e). This css is conducted by fpsc (federal public service commission). Css is a national level exam and every one can participate in it
Pms, pcs and cce are variations of provincial civil service (see i just described p.c.s)
Now to elaborate more: provincial civil service is punjab is more formally called “provincial management service” (p.m.s). Naturally these exams are conducted by ppsc (punjab public service commission)

Similarly when sindh public service commission conducts their own exams then these exams for sindh’s provincial civil service are called c.c.e “combined competitive examinations”

However, for the purpose of simplicity you should associate pcs/pms and cce as the provincial civil service exams of respective province. And css as the national level exams for all pakistani’s

The major difference between css and the provincial civil service examinations (pcs/cce or pms) is that you need domicile of that province to sit in that province’s examinations.