This is the Gnome-OSX-theme with only one difference: nautilus (the file-manager in gnome) is themed with a transparent sidebar all the way up into the titlebar.
To make it look like it on the screenshot:
- Put the window-buttons to the left
(terminal-command: gsettings set org.gnome.desktop.wm.preferences button-layout "close,minimize,maximize:")
- resize the sidebar to its smallest size (all the way to the left) (this aligns the sidebar with the titlebar)
And that's it!
Sometimes (when the transparent area is misaligned) you need to resize your sidebar to the left again.