Modernize RDoc Darkfish template CSS #867

Job	Run time
lint	18s
ruby-versions / Generate Ruby versions	4s
test (3.0, ubuntu-latest)	28s
test (3.0, macos-latest)	23s
test (3.0, windows-latest)	1m 28s
test (3.1, ubuntu-latest)	28s
test (3.1, macos-latest)	31s
test (3.1, windows-latest)	1m 30s
test (3.2, ubuntu-latest)	30s
test (3.2, macos-latest)	22s
test (3.2, windows-latest)	1m 28s
test (3.3, ubuntu-latest)	28s
test (3.3, macos-latest)	22s
test (3.3, windows-latest)	3m 57s
test (head, ubuntu-latest)	32s
test (head, macos-latest)	22s
test (head, windows-latest)	1m 24s
test (jruby, ubuntu-latest)	2m 8s
test (jruby, macos-latest)	1m 40s
test (jruby-head, ubuntu-latest)	2m 2s
test (jruby-head, macos-latest)	1m 13s
test (truffleruby, ubuntu-latest)	2m 22s
test (truffleruby, macos-latest)	2m 7s
test (truffleruby-head, ubuntu-latest)	3m 28s
test (truffleruby-head, macos-latest)	2m 5s
	31m 40s

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