overshoot/undershoot for gtk3 not set

[Johannes Wolf]

Also reported here: https://bugs.launchpad.net/ubuntu/+source/yuyo-gtk-theme/+bug/1471044
Because overshoot and undershoot is not set, they are represented by a ugly white bar (See image in the attachments).
Solution:
Add this to ./gtk-3.0/gtk-widgets.css

/*************
 * overshoot *
 *************/
.overshoot.top {
    background: -gtk-gradient(radial, center top, 0, center top, 0.7, from(shade(@bg_color, 0.92)), to(alpha(@bg_color, 0.0)));
}

.overshoot.right {
    background: -gtk-gradient(radial, right center, 0, right center, 0.7, from(shade(@bg_color, 0.92)), to(alpha(@bg_color, 0.0)));
}

.overshoot.bottom {
    background: -gtk-gradient(radial, center bottom, 0, center bottom, 0.7, from(shade(@bg_color, 0.92)), to(alpha(@bg_color, 0.0)));
}

.overshoot.left {
    background: -gtk-gradient(radial, left center, 0, left center, 0.7, from(shade(@bg_color, 0.92)), to(alpha(@bg_color, 0.0)));
}

/**************
 * undershoot *
 **************/
.undershoot.top {
    background: none;
}

.undershoot.bottom {
    background: none;
}

.undershoot.left {
    background: none;
}

.undershoot.right {
    background: none;
}