Polymer partially polyfills CSS Custom Properties:
<a href="https:&#x2F;&#x2F;www.polymer-project.org&#x2F;1.0&#x2F;docs&#x2F;devguide&#x2F;styling.html#xscope-styling-details" rel="nofollow">https:&#x2F;&#x2F;www.polymer-project.org&#x2F;1.0&#x2F;docs&#x2F;devguide&#x2F;styling.ht...</a><p>Also, for what it&#x27;s worth, not all new JavaScript features are polyfill-able. Proxies, for example, are impossible to polyfill, should they not have been added? WeakMaps are also only partially polyfill-able, are they overdesigned too?