* The Default button style is the same type you see for the OK button in most
dialog boxes: it's outlined with both a thin (one-pixel) line, and with a
thicker line (three pixels thick).
* The Standard style is a rounded rectangle without a shadow. It looks like a
Cancel button: its outline is a single one-pixel line.
* The Oval button style is transparent. Use it to overlay circular or oval
shapes. Although the boundary of an oval button is rectangular, HyperCard
respects its oval shape when tracking the mouse for highlighting and for
messages (mouseEnter, mouseWithin, mouseLeave) and mouse clicks.
A separate article describes another new button style: pop-up button.
This article was adapted from the HyperCard 2.2 New Features stack.