Taking a look at the ULS css the css is inconsistent and incorrectly ordered:
https://git.wikimedia.org/blob/mediawiki%2Fextensions%2FUniversalLanguageSelector/cf52230d3581b69c7ecacfb256e8f95e8f742ae9/resources%2Fcss%2Fext.uls.css
filter and -ms-filter should be at the very start before any of the gradient rules.
-webkit-gradient and -webkit-linear-gradient should be before linear-gradient.
Also -ms-linear-gradient doesn't exist. At least not outside of the preview version of IE10 no-one should be using since IE10 has a real release.
Version: unspecified
Severity: normal