The new CSSOM provides typed style access for developers. This will generally improve performance primarily by removing the need to do lots of string parsing. In addition to this, it will enable performant development of various new Houdini specifications (including custom properties, layout and paint). Only a subset of CSS properties are supported for now: https://chromium.googlesource.com/chromium/src/+/master/third_party/WebKit/Source/core/css/cssom/README.md
Docs: https://developers.google.com/web/updates/2018/03/cssom https://docs.google.com/document/d/1a4gFI-iFv5uA3SskHMrt-ZphCJTbNda9U78xlHmektA/view