A note about style variations
If you are upgrading an existing XenForo site to XenForo 2.3, style variations for existing styles are disabled by default. This is the case even for the "Default style" even if you have never modified it.
To enable variations (dark mode) you would need to go to Admin CP > Appearance > Styles and click the style you wish to enable variations for and click "Enable variations".
This will then make available various style properties which support alternate variations (typically light/dark).
