Add 'todo' field to dark mode settings #2576

Job	Run time
CSS for HTML themes	1m 12s
Julia 1.6 - ubuntu-latest - x64	4m 40s
PDF/LaTeX backend	4m 16s
Julia 1.6 - macos-latest - x64	8m 39s
Documentation: html	1m 28s
Julia 1.6 - windows-latest - x64	11m 32s
Linkcheck: online tests	1m 56s
Documentation: pdf	3m 9s
Julia 1 - ubuntu-latest - x64	3m 15s
Linkcheck: Documenter manual	4m 58s
NodeJS for prerender	1m 36s
Julia 1 - macos-latest - x64	7m 33s
Prettier (JS code formatting)	4s
Julia 1 - windows-latest - x64	4m 52s
Julia nightly - ubuntu-latest - x64	4m 52s
Julia nightly - macos-latest - x64	9m 42s
Julia nightly - windows-latest - x64	6m 26s
Julia 1 - ubuntu-latest - x86	4m 5s
	1h 24m 15s

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