How to Override CSS styles for an existing application

Hello Guys,

I have developed an asp.net application without any css styles.
Now I would like to concentrate on some attractive UI design.
Problem is I have 100s of pages So I dont want to apply css style for each and every controls

I need some animation effects also using JQuery.

for eg. Old version of csharp corner and new version of csharp corner

Note : I have used most of the ASP.NET controls

Any thoughts?

Regards,
N