borderColor: String

Sets the border color of Range Buttons. Values of borderColor can be specified in “HTML Color Name”, “hex code” or “rgba values”

Default: “#2196f3” (varies based on themes)
Example: “blue”, “#41a5f5”, … 
var stockChart = new CanvasJS.StockChart("container",
{
 .
 .
 rangeSelector: {
   buttonStyle: {
     borderColor: "#41a5f5",
     .
     .
   },
 },
 .
 . 
});
stockChart.render();
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