drop list with check box

HansVogelaar Piggy-backing off this; hope no one minds.

This is great and works beautifully, but I have a question: what if I wanted two different lists to work like this. For instance, range C2:C101 would have the data validation range H2:H10 and range D2:D101 would have the data validation range I2:I15. 

So, someone would select option(s) from the drop-down list in C3, and I'd like for them to have the ability to select more than one option from the range of H2:H10. Same thing with the drop-down list in D4. 

VBA is not my strong suit, unfortunately. I'm much more proficient in JS, which at least gives me the base to understand what's happening in the code you provided, but not enough to expound upon it. I'd love a little help, if you wouldn't mind!

Thanks!