OptionButton.BackStyle Property (Outlook Forms Script)
Returns or sets an Integer that specifies the background style for an object. Read/write.
expression A variable that represents an OptionButton object.
The possible values are 0 and 1. 0 represents the background as transparent, 1 represents the background as opaque.
The BackStyle property determines whether a control is transparent. If BackStyle is 1, the control is not transparent and you cannot see anything behind the control on a form. If BackStyle is 0, you can see through the control and look at anything on the form located behind the control. The BackColor property is only valid if the BackStyle property is set to 1.
BackStyle does not affect the transparency of bitmaps. You must use a picture editor such as Paintbrush to make a bitmap transparent. Not all controls support transparent bitmaps.