Merge latest css improvements into master #435

Job	Run time
B2 gcc-11	3m 6s
B2 msvc-14.2	5m 11s
B2 clang-14	3m 16s
CMake gcc-11 17 Debug	6m 50s
B2 msvc-14.3	4m 27s
CMake gcc-11 20 Release	7m 34s
CMake clang-11 17 Debug	4m 48s
CMake msvc-14.2 Debug C++17	7m 14s
CMake clang-11 20 Debug	4m 41s
CMake msvc-14.2 Release C++17	7m 0s
CMake clang-13 17 Release	6m 17s
CMake msvc-14.3 Debug C++20	6m 18s
CMake clang-13 20 Release	6m 13s
CMake msvc-14.3 Release C++20	6m 35s
CMake clang-14 17 Debug -stdlib=libc++	6m 40s
CMake clang-14 20 Release -stdlib=libc++	8m 20s
	1h 34m 30s

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