How do I style select options?

I have options for a select field from 2 sources (this years options and last years options). In the drop down list I would like to distinguish the options between the sources (e.g. this years options with a green background, last years with a pink background).

I think you have to use a Javascript library to create a custom select box like that. The browser's select box does not allow you to do that.

For example, something like this provides a ton of flexibilty: https://joshuajohnson.co.uk/Choices/ or https://slimselectjs.com/

Thanks