How to change bar labels font in Graph Builder Stacked Bar Chart?

[#1]

I made the following stacked bar chart in Graph Builder. As you can see, the labels in the bars are hard to read. How can I adjust that font? Bold, White would make them visible. I couldn't find an option in Graph > Customize.

[#2]

This is a question that was previously asked.  

Change (Increase/Decrease) Font size for Value Labels in Graph Builder charts