Dark Theme Is Better For Your Eyes, Install GnomishDark theme in Ubuntu 14.10/14.04

Install GnomishDark theme in Ubuntu 14.10 Utopic/14.04 Trusty/Ubuntu 12.04 Precise/Linux Mint 17.1/17/13 (GTK)

GnomishDark is dark clean GTK3 theme, this theme is based on adwaita engine, and Gnome-Shell version is also included with this theme but only available for Ubuntu 12.04. GnomishDark also offers GTK2 themes, which depends on murrine and pixbuf engines. Developer stopped development of Gnome Shell theme because Gnome Shell development is frequent and always breaks his theme so no more gnome updates. If you found any bug in theme then report it to developer via given source link.

Gnome 3.6/3.4 Screenshots

You can use Unity Tweak Tool, Gnome-tweak-tool or Ubuntu-Tweak to change themes.

To install GnomishDark theme in Ubuntu/Linux Mint open Terminal (Press Ctrl+Alt+T) and copy the following commands in the Terminal:

Terminal Commands:
sudo add-apt-repository ppa:noobslab/themes
sudo apt-get update
sudo apt-get install gnomishdark

To fix software center text issue enter these commands in terminal:

Terminal Commands:
cd /usr/share/software-center/ui/gtk3/css/ && sudo mv softwarecenter.css softwarecenter.css.backup
cd /usr/share/software-center/ui/gtk3/art/ && sudo mv stipple.png stipple.png.backup
cd && wget -O softwarecenter.css http://drive.noobslab.com/data/themes/delorean-dark-3.10/softwarecenter.css
sudo mv softwarecenter.css /usr/share/software-center/ui/gtk3/css/
cd && wget -O stipple.png http://drive.noobslab.com/data/themes/delorean-dark-3.10/stipple.png
sudo mv stipple.png /usr/share/software-center/ui/gtk3/art/

To revert back software center theme simply enter these commands:

Terminal Commands:
cd /usr/share/software-center/ui/gtk3/css/ && sudo mv softwarecenter.css.backup softwarecenter.css
cd /usr/share/software-center/ui/gtk3/art/ && sudo mv stipple.png.backup stipple.png

That's it

Source: GnomishDark