May be set to one of normal, active, or disabled.
In a dialog box, one button may be designated the
“default”
button (meaning, roughly,
“the one that gets invoked when the user presses <Enter>”).
active indicates that this is currently the default button;
normal means that it may become the default button, and
disabled means that it is not defaultable.
The default is normal.
Depending on the theme, the default button may be displayed
with an extra highlight ring, or with a different border color.