I received these errors using the W3c validator, but the colors work fine on my website. Why do they report errors and what should the colors be to be the same?

W3C CSS Validator Result Errors

Line: 5 Context : BODY
Property scrollbar-highlight-color doesn't exist : #6699cc
Line: 6 Context : BODY
Property scrollbar-arrow-color doesn't exist : #006666
Line: 7 Context : BODY
Property scrollbar-shadow-color doesn't exist : #006666