Why does this matter so much? Our team purposefully decided to use a really well known component library (Material UI React) so that it automatically takes care

Why does this matter so much? Our team purposefully decided to use a really well known component library (Material UI React) so that it automatically takes care of browser inconsistencies. But no, I still find myself and my team scratching our heads writing a ton of Safari-specific CSS just to ensure it works on par with Firefox.