I want this transparency effect. Only the transparency, don’t care about other elements.
All I know is I can set buttons to down all opacity of a window, but it includes text and icons. That install only lowers the background and nothing else. This is from a theme called Arch but after installing I still have opaque windows.
BTW, why they have 2 toolbars? One is the task manager and another one on top.
They are probably use a kvantum theme for the transparency.
There is no way to know without asking them but it look like they are using global menus so maybe they felt it was too crowded with everything in one?
You can have as many panels as you want. Why would you want more than one? I don’t know. Personally, if I’m using a mouse, I don’t like to have a panel on the top.
And I like my panels on the side (preferably the right side) because I have a widescreen monitor and the vertical space is precious. All in what we have and what we like 
I like transparency too!