The best thing about this release is CSS Variables support: https://developer.apple.com/library/mac/releasenotes/General/WhatsNewInSafari/Articles/Safari_9_1.h

The best thing about this release is CSS Variables support: https://developer.apple.com/library/mac/releasenotes/General/WhatsNewInSafari/Articles/Safari_9_1.html#//apple_ref/doc/uid/TP40014305-CH10-SW12 https://developer.apple.com/library/mac/releasenotes/General... CSS variables are a great way to do theming and cross-scoped styling for Custom Elements and shadow DOM. Polymer's had a shim for this for a while, but native support is much faster and more flexible.