Improve Visibility of Category Titles and Selection in Dark Mode

In dark mode, the category separator titles are not sufficiently visible, making them difficult to read. Additionally, when a user selects a category with the mouse, there is not enough contrast or visual indication to distinguish that the category is selected. This can cause confusion and a less fluid user experience.

The style of the separator titles should be adjusted, and the category selection state should be improved to ensure they are clearly visible and easy to identify, even in dark mode. This will help enhance accessibility and interaction with the interface.