Re: border-color adds a new border in GtkScrolledWindow (GTK 3.18) ?

[Giovanni Panozzo <giovanni panozzo it>]

It seems to be a "undershoot" appearing when I set the background-color 
on the GtkScrolledWindow.

Whith the following workaround, the undershoot hides again:

#myscrolledwindow {
        background-color: green;
}

#myscrolledwindow.undershoot {
        background: none;
}


But:
- what really is undershoot and overshoot ? I cannot find any
  documentation.
- why does it appears starting from GTK 3.18 when setting the
  background-color in the GtkScrolledWindow ?