Can be installed from Gnome look website, extracted to .themes directory, set in Tweaks app
Recently spent some time trying to customize themes even further. Custom CSS can be added in the .config/gtk-3.0/gtk.css file, or modified within the active theme folder (/usr/share/themes if built-in, ~/.themes if manually installed).
Extensions
Can be installed directly from website with the click of a slider
Current Settings
Shell and applications: cyan Solarized theme
Cursor: Breeze_Snow
Icons: Breeze
Extensions
Alternatetab
Dash to dock
Open weather
Transparent window
Other Gnome Specific Apps
Variety: manages a background slideshow, and customized clock on home screen. See current installation for settings.