Thanks for feedback!

To not lose data, make sure that an option "Warn about unsaved changes" is active in the settings (it should be active by default) - this way a warning will be shown when trying to reload the page with unsaved changes.

Dark themes might be implemented differently on different sites, that's why it's possible to set up different colors for marking text in the extension settings or in the mouse context menu.

If the problems are still present or you have other ideas to improve this extension, you could always share detailed information: there are a support mail address and a link to GitHub in the More Information section on the Extension page.