Update forms.css

Remove code line 64 the 'important'.
You can view specific issues #26: Form of Select has an UI change problem,A rule that has the !important property will always be applied no matter where that rule appears in the CSS document.
I think that you can not use the '! important' here.
remove 'important' can solve this problem.
My English is not very good, I hope I expressed clearly.
thanks!