Modernize RDoc Darkfish template CSS #859

Job	Run time
lint	16s
ruby-versions / Generate Ruby versions	2s
test (3.0, ubuntu-latest)	25s
test (3.0, macos-latest)	27s
test (3.0, windows-latest)	1m 29s
test (3.1, ubuntu-latest)	26s
test (3.1, macos-latest)	26s
test (3.1, windows-latest)	1m 31s
test (3.2, ubuntu-latest)	26s
test (3.2, macos-latest)	34s
test (3.2, windows-latest)	1m 38s
test (3.3, ubuntu-latest)	24s
test (3.3, macos-latest)	26s
test (3.3, windows-latest)	2m 51s
test (head, ubuntu-latest)	35s
test (head, macos-latest)	25s
test (head, windows-latest)	1m 19s
test (jruby, ubuntu-latest)	1m 53s
test (jruby, macos-latest)	1m 33s
test (jruby-head, ubuntu-latest)	1m 54s
test (jruby-head, macos-latest)	1m 18s
test (truffleruby, ubuntu-latest)	2m 23s
test (truffleruby, macos-latest)	1m 49s
test (truffleruby-head, ubuntu-latest)	3m 18s
test (truffleruby-head, macos-latest)	2m 42s
	30m 30s

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