artwork/usr/share/themes/Lubuntu-default/gtk-3.0/gtk-widgets-radiance.css

/* Set up shadows and hilights for button visual separation */
.primary-toolbar .linked .button,
.primary-toolbar .button.raised.linked,
.primary-toolbar .raised.linked .button {
    box-shadow: inset 1px 0 shade (@dark_bg_color, 1.1),
                inset -1px 0 shade (@dark_bg_color, 0.9);
}

.primary-toolbar .linked .button:first-child,
.primary-toolbar .button.raised.linked:first-child,
.primary-toolbar .raised.linked .button:first-child {
    box-shadow: inset -1px 0 shade (@dark_bg_color, 0.9);
}

.primary-toolbar .linked .button:last-child,
.primary-toolbar .button.raised.linked:last-child,
.primary-toolbar .raised.linked .button:last-child {
    box-shadow: inset 1px 0 shade (@dark_bg_color, 1.1)
}

.primary-toolbar .linked .button:active,
.primary-toolbar .button.raised.linked:active,
.primary-toolbar .raised.linked .button:active {
    box-shadow: inset 1px 0 shade (@dark_bg_color, 0.9);
}

.primary-toolbar .linked .button:insensitive,
.primary-toolbar .button.raised.linked:insensitive,
.primary-toolbar .raised.linked .button:insensitive {
    box-shadow: inset -1px 0 shade (@dark_bg_color, 0.9);
}

.primary-toolbar .linked .button:backdrop:last-child,
.primary-toolbar .button.raised.linked:backdrop:last-child,
.primary-toolbar .raised.linked .button:backdrop:last-child {
    box-shadow: inset 1px 0 shade (@dark_bg_color, 1.1);
}

.menubar {
    color: @dark_fg_color;
    text-shadow: 0 1px shade (@dark_bg_color, 1.1);
}

.menubar.menuitem:hover,
.menubar .menuitem:hover {
    color: @selected_fg_color;
    text-shadow: 0 1px shade (@selected_bg_color, 1.1);
}

.menuitem:hover,
.menu .menuitem:hover {
    color: @selected_fg_color;
    text-shadow: 0 -1px shade (@selected_bg_color, 0.7);
}

.menuitem:insensitive,
.menuitem *:insensitive {
    color: mix (@fg_color, @bg_color, 0.5);
    text-shadow: 0 1px shade (@bg_color, 1.14);
}

/* primary-toolbar */
.primary-toolbar,
.primary-toolbar .toolbar,
.primary-toolbar.toolbar {
    background-image: -gtk-gradient (linear, left top, left bottom,
                                     from (shade (@dark_bg_color, 0.96)),
                                     to (shade (@dark_bg_color, 1.1)));
    border-bottom-color: shade (@dark_bg_color, 1.02);
    border-top-color: shade (@dark_bg_color, 1.02);

    text-shadow: 0 1px shade (@dark_bg_color, 1.1);
}

.primary-toolbar :insensitive {
    text-shadow: 0 1px shade (@dark_bg_color, 1.1);
}

.primary-toolbar GtkComboBox,
.primary-toolbar .button *,
.primary-toolbar .button {
    text-shadow: 0 1px alpha (shade (@dark_bg_color, 1.25), 0.32);
}

.primary-toolbar .raised .button,
.primary-toolbar .raised.button,
.primary-toolbar .button:hover,
.primary-toolbar .button:active,
.primary-toolbar .button:insensitive {
    background-image: -gtk-gradient (linear, left top, left bottom,
                                     from (shade (@dark_bg_color, 1.03)),
                                     to (shade (@dark_bg_color, 0.96)));
}