Hello Sai,

I think you mean CSE, CS, and CST. Most universities have the same meaning for CSE, CS and CST. However, in some universities CS is a Science course while CSE/CST are engineering courses. If you could mention the universities/colleges in which you have confusion in maybe we'll be able to help. Apart from a little difference in syllabus there is no difference.

Also CSS is a programming language and not related to a degree/diploma.

Hope this helps.