Weird Rendering on Mac

Hello,

This is rather a weird one which i cannot not explain.

Any browser on my Mac will render my responsive theme very differently to any browser on my windows machine.

Let me start by saying this was after backing up my 6.3 theme in full, deleting it and installing 8.7. After having installed 8.7, i was not a fan of the new framework and admin area layout. So i decided to delete this theme and restore the backup for 6.3.

Once restored, the theme loaded and rendered on my windows machine exactly as it was before the update. On the Mac, it looks as though it is rendering from the new framework, even thought these files no longer exist.

I have attached to screen shots.

Any ideas ?

Thanks

Roy