How to make window frame thinner

[Martin Cigorraga]

Hello,

Please let me know if I should address this question to another list.

I recently discovered Lollypop music player - a very neat one - and now I'm
intrigued if there's a way to make the top part of the window frame thinner
as shown in Lollypop's screenshots: https://gnumdk.github.io/lollypop/

Here is a screenshot of a fresh installed Lollypop on a Fedora 22 / GNOME
3.16.2 using default Adwaita theme: https://i.imgur.com/Ntw9RFP.png

As you see, it is considerably bigger - taking away a lot of my laptop's
screen real-state.

Could you please point me on how to set it in a smaller fashion to
replicate Lollypop's screenshots look and feel?

Many thanks,
-Martin