I know right! the only annoying part is when you have to guess random countries cause all the black is gone and they are just encompassesd in other countries. For example I missed Djibouti because I had already guessed Ethiopia.
The instructions are unclear. You said "highlighted" but "random". So what does that mean? I tried inputting both highlighted and unhighlighted and nothing happened. Therefore leaving this comment to let you know
The countries that are highlighted are highlighted along with their neighbors. for example, if I see panama, colombia and costa rica highlighted, but not nicaragua nor peru, then I know one of the countries is panama and not colombia