To set custom border settings specific to the 'selected' state for all series at once, use the properties of the commonSeriesSettings.selectionStyle.border configuration object.
To set custom border settings specific to the 'selected' state for all series of a single type at once, use the properties of the corresponding object within commonSeriesSettings (e.g. area.selectionStyle.border). The values that are set within this object override the corresponding common values that are set within the root commonSeriesSettings.selectionStyle.border object.
In case you have to set a border selection style property for an individual series, use the selectionStyle.border object within the series object of the series array. The values that are set individually override corresponding common values.
The following dash styles are available:
The border is a solid, continuous line.
The border is displayed using long dashes.
The border is displayed using dashes.
The border is displayed using dots.
Any combination of 'longDash', 'dash' and 'dot'
The border is displayed by repeating the specified combination. For instance, 'dashdotdash'.