add light/dark theme with theme switch injected in page (wip) #776

Job	Run time
Julia 1.6 - ubuntu-latest - x64	3m 33s
Julia 1.6 - macOS-latest - x64	3m 48s
build	2m 20s
Julia 1.6 - windows-latest - x64	11m 55s
Julia 1 - ubuntu-latest - x64	2m 39s
Julia 1 - macOS-latest - x64	3m 41s
Julia 1 - windows-latest - x64	3m 31s
Julia nightly - ubuntu-latest - x64	4m 38s
Julia nightly - macOS-latest - x64	5m 38s
Julia nightly - windows-latest - x64	7m 3s
	48m 46s

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