Modernize RDoc Darkfish template CSS #866

Job	Run time
lint	15s
ruby-versions / Generate Ruby versions	3s
test (3.0, ubuntu-latest)	33s
test (3.0, macos-latest)	21s
test (3.0, windows-latest)	1m 30s
test (3.1, ubuntu-latest)	26s
test (3.1, macos-latest)	23s
test (3.1, windows-latest)	1m 19s
test (3.2, ubuntu-latest)	30s
test (3.2, macos-latest)	24s
test (3.2, windows-latest)	1m 35s
test (3.3, ubuntu-latest)	23s
test (3.3, macos-latest)	30s
test (3.3, windows-latest)	2m 2s
test (head, ubuntu-latest)	31s
test (head, macos-latest)	28s
test (head, windows-latest)	1m 21s
test (jruby, ubuntu-latest)	1m 56s
test (jruby, macos-latest)	1m 51s
test (jruby-head, ubuntu-latest)	1m 56s
test (jruby-head, macos-latest)	1m 27s
test (truffleruby, ubuntu-latest)	2m 22s
test (truffleruby, macos-latest)	2m 1s
test (truffleruby-head, ubuntu-latest)	3m 18s
test (truffleruby-head, macos-latest)	2m 38s
	30m 3s

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