My CSS file is in :
Project/Web/Support/Styles/file.css
My image is in :
Project/Web/images/image.png
I want this image in my CSS file.
Your css is here: Project/Web/Support/Styles/file.css
1 time ../ means Project/Web/Support and 2 times ../ i.e. ../../ means Project/Web
../
../../
Try:
background-image: url('../../images/image.png');