Selected-Tab Hard to Distinguish in Default Ambiance Theme

[Lonnie Lee Best]

The default Theme in Ubuntu 16.04 is called "Ambiance":
http://neartalk.com/ss/2016-03-16_005_565x390.png

When Gnome-System-Monitor is running under the Ambiance theme, you can barely distinguish which tab is selected:
http://neartalk.com/ss/2016-03-16_003_679x497.png

Compare this with the non-default theme called "Radiance", where the selected-tab (in Gnome-System-Monitor) is clearly distinguishable at a glance (without eye strain):
http://neartalk.com/ss/2016-03-16_004_687x497.png

Which package would be responsible for making the selected-tab more distinguishable to the eye in gnome-system-monitor under the default Ambiance theme?

ProblemType: Bug
DistroRelease: Ubuntu 16.04
Package: gnome-system-monitor 3.18.2-1
ProcVersionSignature: Ubuntu 4.4.0-13.29-generic 4.4.5
Uname: Linux 4.4.0-13-generic x86_64
ApportVersion: 2.20-0ubuntu3
Architecture: amd64
CurrentDesktop: Unity
Date: Wed Mar 16 04:38:11 2016
InstallationDate: Installed on 2016-03-14 (1 days ago)
InstallationMedia: Ubuntu 16.04 LTS "Xenial Xerus" - Alpha amd64 (20160307)
SourcePackage: gnome-system-monitor
UpgradeStatus: No upgrade log present (probably fresh install)

[Jeremy Bícha (jbicha)]

Ubuntu-themes is the source package now.

[Eugene Romanenko (eros2)]

It little bit hard to distinguish active tab from inactive tabs in Nautilus.

For example, in Adwaita theme, current tab underlined with theme selection color and clearly visible. Please add such pronounce in Ambiance/Radiance.

[Eugene Romanenko (eros2)]

Digged little bit into gtk3 css-ing and created workaround:

Add to ~/.config/gtk-3.0/gtk.css:

.nautilus-window notebook tab:checked {
    background-image: linear-gradient(to top, @selected_bg_color, alpha(@bg_color, 0) 3px);
}

Active tab will be underlined with theme color. Remove ".nautilus-window" to affect any tabs, not just content tabs in Nautilus window.

Works in 18.04.