unity.css

/* My custom /usr/share/themes/Ambiance/gtk-3.0/apps/unity.css */
/* Remember to switch in your user name in the url below! */

UnityPanelWidget,
.unity-panel {
    background-image: url("file:///home/USERNAME/Pictures/frame.png");

    color: @dark_fg_color;

    -unico-border-gradient: none;
}

.unity-panel.menubar,
.unity-panel .menubar {
}

.unity-panel.menuitem,
.unity-panel .menuitem {
    border-width: 1px 1px 0 1px;

    icon-shadow: 0 -1 shade (@dark_bg_color, 0.7);
}

.unity-panel.menubar.menuitem:hover,
.unity-panel.menubar .menuitem *:hover {
    background-image: -gtk-gradient (linear, left top, left bottom,
                                     from (shade (@dark_bg_color, 1.7)),
                                     to (shade (@dark_bg_color, 1.12)));

    color: shade (@dark_fg_color, 1.1);

    -unico-border-gradient: -gtk-gradient (linear, left top, left bottom,
                                           from (shade (@dark_bg_color, 1.08)),
                                           to (shade (@dark_bg_color, 0.98)));
    -unico-inner-stroke-gradient: -gtk-gradient (linear, left top, left bottom,
                                                 from (shade (@dark_bg_color, 1.8)),
                                                 to (shade (@dark_bg_color, 1.16)));
}