shulker_box_tooltip_dark.png.zip

Dark version of the tooltip using the same color palette of the Default Dark Mode resource pack (zipped version in case the image is compressed by github)

Would be nice to have an option to enable dark mode

The feature has been added, thank for the suggestion!
It will be available in the 1.16.3 release as a config option.
The mod can also use the dark mod setting from LibGui if installed.