dropShadow
enabled: Boolean
Enable a dropshadow for paths of the SVG
enabledOnSeries: Array of Numbers
Provide series index on which the dropshadow should be enabled.
top: Number
Set top offset for shadow
left: Number
Set left offset for shadow
blur: Number
Set blur distance for shadow
color: String || Array of Strings
Give a color to the shadow. If array is provided, each series can have different shadow color
opacity: Number
Set the opacity of shadow.