REVERT: Remove @host and other legacy CSS no longer used

Note about Dartium: Dartium by default doesn't support the newer rules; to turn on the support, the "Experimental Web Platform features" flag has to be turned on in chrome://flags. (reverted from commit ed02ffb30a3ae79455db4d32bf90072c50b9fa2d)
Merge pull request #724 from ussuri/revert-remove-legacy-css-rules

REVERT: Remove @host and other legacy CSS no longer used