Applies to Combined Bar/Line charts.
By default, combined charts show one dimension as bars, and the second dimension as a line. The second option can be specified as an area chart, instead.
To make this change,
Click Settings on the right side of the Visuals menu.
The Settings modal window appears.
Select Convert Line to Area Visual, and click Apply.
Click Refresh Visual.
Notice that the chart changed from bar/line to bar/area.