I have a bar chart, which has a pop-up pie chart (showing some more granular information) in a tooltip.
This works well, except I don't seem able to change the thick border surrounding the pop-up chart (image attached). I've tried configuring the various borders (tooltip on the main chart, chartArea on the pop-Up chart etc..), but nothing makes any difference. What do I need to set to reduce the border thickness?
The main chart tooltip is defined here:-
The tooltip template here:-