This property is used to choose the composition mode for the background mask effect.
The default value is destination-out, which unveils the background below using drawn elements, any other valid value
can be found here
The cover property can be set to a HEX string or to a color object, that is the same as the one used
in particles.color options.
The cover can also be a object like the one described below.
This property set the background mask mode, this mode enables the composite option to all elements drawn.
The options to apply a base color to canvas to cover what's behind The particles will unveil what is covered by the canvas