Duplicate of #31
There is a window control missing in 7.css, but present in XP.css and 98.css .
There's a question mark button in windows, windows 7 included.
Examples:
VirtualBox:

Internet Options:

Its older function is when pressed, show information about a certain element after the element was clicked.
Its newer function is just to open the help program when clicked.

Direct rip of window decor graphics from the theme file:

#31 (comment)