From what I can see on your attached image, the Border that is causing problems to you is the PlotArea border, not the Chart's one. The plot area is part of the chart area and is represented by the ClipPanel control. You may easily create a style , targeting the ClipPanel and set its Border to be Transparent and the BorderThickness to 0. You can find more information and a code sample in this help topic. Copy-paste the style and delete the Background setter. Instead set the Border and BorderThickness I mentioned.
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