The CSSRulePlugin won't be phased out any time soon. Using CSS variables is just a suggestion. However, IE was phased out years ago.   And animating CSS variables won't cause an error in IE, so why are you even worried about IE? Nobody uses IE except for South Koreans, and that's only because it's the law for their banking apps.   An old article, but the Active X situation remains.   https://www.zdnet.com/article/south-koreans-use-internet-explorer-its-the-law/
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