Active application's button isn't highlighted on the panel

[Oleg Moiseichuk]

When using Radiance theme in Gnome Flashback session in 16.04 LTS, active application's button is not highlighted on the panel. In Ambiance theme active application's button is highlighted by the darker color. Comparison of the gnome-panel.css in /usr/share/themes/Ambiance/gtk-3.0/apps and /usr/share/themes/Radiance/gtk-3.0/apps showed the absence of some code in Radiance theme.
Adding the fragment of code from Ambiance gnome-panel.css to Radiance respective file fixes the issue (possibly some adjustment of values is needed, as this code is related to dark Ambiance theme, rather than light Radiance theme).
Here's the mentioned code fragment:

PanelApplet .button:checked {
    background-image: -gtk-gradient (linear, left top, left bottom,
                                     from (shade (@dark_bg_color, 0.95)),
                                     to (shade (@dark_bg_color, 1.1)));
}

PanelApplet .button:checked:prelight {
    background-image: -gtk-gradient (linear, left top, left bottom,
                                     from (shade (@dark_bg_color, 1.15)),
                                     to (shade (@dark_bg_color, 1.3)));
}

PanelApplet .button:checked:prelight:active {
    border-image: none;
    background-image: -gtk-gradient (linear, left top, left bottom,
                                     from (shade (@dark_bg_color, 0.75)),
                                     to (shade (@dark_bg_color, 0.9)));
    border-color: shade (@dark_bg_color, 0.8);
}

[Launchpad Janitor (janitor)]

Status changed to 'Confirmed' because the bug affects multiple users.