styles are not setting from same name css file

Hi,

My use case is as follows:

I have one library project which have css file with name x and i set some
styles here .

Now i create the same styles structure in main application project with
same name of css file and set part of styles here.

when i run my application then styles (Like Alert/Button class level styles)
are apply which are set in main application css file, but if i set same
styles(Like Alert/Button class level styles) in library css file then
theses styles are not applying. to apllication.

Is there any heirarchy issue ..or best way to ovevride css file styles.