[Feature] Dropdown Checkboxes for theme options

[SpaceEnergy]

Before Requesting

• [X] I found no existing issue matching my feature request
• [X] This request is related to Millennium, and not a request for a specific theme/addon

Describe the feature you'd like!

Dropdown with checkboxes inside which the user can select according to his wishes. of course, the individual options should also be bound to a CSS or JS file

like this:

Anything else?

No response