Options for the point markers of line and scatter-like series. Properties
like fillColor, lineColor and lineWidth define the visual
appearance of the markers. The symbol option defines the shape. Other
series types, like column series, don't have markers, but have visual
options on the series level instead.
In styled mode, the markers can be styled with the .highcharts-point,
.highcharts-point-hover and .highcharts-point-select class names.