paper-gtk-theme/Paper/gtk-3.0/widgets/menu-button.css

/* Copyright 2014 Sam Hewitt.
*
* This file is part of the Paper GTK theme.
*
* The Paper GTK theme is free software: you can redistribute it
* and/or modify it under the terms of the GNU General Public License as
* published by the Free Software Foundation, either version 3 of the
* License, or (at your option) any later version.
*
* The Paper GTK theme is distributed in the hope that it will be
* useful, but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General
* Public License for more details.
*
* You should have received a copy of the GNU General Public License along
* with the Paper GTK theme. If not, see http://www.gnu.org/licenses/.
*/

/***************
 * Menu Button *
 ***************/

.menu.button {
    background-image: none;
    background-color: @base;
    border: 1px solid @selection;
}

.menu.button.separator {
    border-style: none;
    color: shade(@foreground, 3.2);
    -GtkMenuItem-horizontal-padding: 0;
    -GtkWidget-separator-height: 1;
}

.menu.button:hover {
    background-image: none;
    background-color: @base;
    color: @foreground;
    border-style: none;
}

.menu.button:insensitive {
    background-color: @base;
    color: lighter(@internal_element);
    border-style: none;
}

.menu.button:hover,
.menu.button:active,
.menu.button:active:insensitive,
.menu.button:insensitive,
.menu.button {
    border-width: 0;
    background-color: shade(@foreground, 1.05);
    background-image: none;
}


GtkMenuButton.button:active,
GtkMenuButton.button.raised:active {
    color: @foreground;
}

.button.menuitem.menubar:active {
    background-image: none;
    background-color: @background;

    border: 1px solid @background;
    border-radius: 0 0;
    border-image: none;
    border-bottom-width: 0px;
}

.button.menuitem.menubar *:active,
GtkMenuButton.button *:active,
.toolbar GtkMenuButton.button *:active {
    color: @foreground;
}

GtkMenuButton .menu {
}