Hi, I have a 96 civic and I need your help how make the tire perpendicular to the ground. I already replaced the spring and strut(in both side on the rear) but still tilting inward. Thanks for the help in advance. This car was stock, no modification done.

 

are you sure the back wheels dont have a camber kit installed?
it sounds like you have some negative camber. Bent control arms?

 

1. That is negative camber. (just letting you know the term for it)
2. When you replaced the struts and springs, you should have gotten an alignment. Did you get one? (Camber isn't adjustable on Civics unless you get a camber kit though)
3. are the new parts OEM style, or is your car lowered at all?
4. It's not supposed to be perpendicular to the ground. You need to have a little negative camber. Though, you do need to go get an alignment if you didn't, to fix the possible toe problems you might have.
5. If you got an alignment, have you noticed any unusual tire wear? If not, then the camber is probably fine.

If everything was installed correctly, you're not lowered, and you got an alignment, you might have a bent suspension part as brichguitars mentioned.