This is accessibility issue.

There are several point to improve:

1. Preselected time zone (Europe - Amsterdam) have not enough contrast and seems like
   

2. Group item like "Africa" have not enough contrast and is not recognizable even if it is disabled item.
   

3. Aria-label of combobox is "search for option" and have to be instead "Search for time zone"
   

4. strong timezone have to be a label for Select