You now have access to Dark Mode theme and Style for forum appearance.
Scroll all the way to the bottom of the forum page and find the setting in the left corner:
Select System to match the theme of your device or browser.
Select Light for normal or daytime use.
Select Dark to reduce eye strain at night as well as blue light wavelength output.
Styles are currently experimental and we're entertaining the idea of having different Style for different holidays or occasions.