Make /deep/ behave like the descendant combinator " " in CSS live profile; effectively no-op. See "Intent to Remove" thread for more details: https://groups.google.com/a/chromium.org/d/topic/blink-dev/HX5Y8Ykr5Ns/discussion https://www.w3.org/TR/selectors-4/#profiles CSS live profile = CSS selector used in CSS file or inside of <style>. CSS snapshot profile = CSS selector used in JS, such as querySelector(..)