The gradient is there and consistent in Safari and Firefox.
Chrome has issues with CSS3 gradients. When they will fix that is anyone's guess since the seem more interested in running up version numbers that actually fixing things.
Internet Explorer, is, well, Internet Explorer. Standards compliance is not in Microsoft's vocabulary - never has been. On gradients, MS requires you to create complex, obtuse filters.
The only way to get around this would be to create a repeating PNG gradient image that could be used instead of CSS3 gradients, but that would require the Custom Design Upgrade to implement. You know, go back to mid 00's technology so MS and Chrome don't blow up?