How to remove borders between series on APEX stacked area charts?

Hey all,

In APEX 19.1, I've created a stacked area chart. In between each series is a white border that I'd like to remove, but I can't find a way to hide it in the APEX interface. In the resulting HTML of the APEX page, it looks like the chart is rendered using SVG. The element that creates the border is a polyline like:

<polyline points="11.2 320 ..." fill="none" stroke="#FFFFFF" stroke-width="1.25"></polyline>

Since the stroke color and width are hard-coded, I thought I'd try adding this to the Appearance->CSS Classes section of the chart region:

polyline: { style="stroke-opacity:0" }

..but that has no effect. That bit of CSS doesn't show up in Firefox's inspector, so that seems to point to me doing something wrong.

Thoughts, anyone?
Rich

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