Thanks so much for your reply, Shin.
It looks like you got it but I am unable to reproduce your results. Would you mind sending me a screenshot of your final state for each marks card?
Also, can you explain how/why your solution works? For example, I notice you are using continent on detail. Was that deliberate?
Tableau Public does not allow opening of attachment.
Many thanks again for helping!
I did not clean up the fields in detail shelf, but I guess the key is that "country" should be put above "Histogram color".
I recommend that you download free trial to understand the background with opening the attached workbook.
Other than that, I cannot answer each tiny question.
And please mark my answer as correct if that works.
That did the trick. Thank you my friend