The two shadow-piercing combinators have been deprecated as stated in https://www.chromestatus.com/features/6750456638341120
Then what's the substitude for achieving the same thing, or this shadow-piercing feature has been completely abandoned?
::shadow
and /deep/
were removed for breaking encapsulation.
The substitutes are:
:host-context
. Read here: http://www.html5rocks.com/en/tutorials/webcomponents/shadowdom-201/