Hi there,
Thank you for contacting us!
This feature is not available in Highcharts as a standard API option. But it can be created with Highcharts.SVGRenderer. Basically, you have to create a custom SVG path and find its correct position on the chart. In that case, I have tried to make it as responsive as possible so let me know if you are happy with the solution, or whether it needs some tweaking.
DEMO: https://jsfiddle.net/BlackLabel/tuhd2vyc/
SVG Renderer: https://api.highcharts.com/class-refere ... VGRenderer
Best regards!