Assertions:
Opera 5.0 used the background color/image of the parent as the default face for the button (unless set by CSS for the button of course.) Opera 6 uses the system user interface color designated for button faces as IE and Netscape does.

Plain Button element :
filler text filler text

Button element embedded in table, no background:
filler text
Cell 2
filler text

Button element embedded in table, table has bgcolor=green:
filler text
Cell 2
filler text

Button element embedded in table, table has background image (crosshair.gif):
filler text
Cell 2
filler text