How-to decrease gnome title-bar height

I've started using Firefox again, and after some time I noticed that Gnome window title-bars were eating a lot of screen space.

To solve the issue, I've tried installing a plugin, but I was not too happy with the result (even after some custom tweaks).
Later, I gave up with the plugin, and started searching for other solution, reading various sources (like forums).

Finally, a good hint appeared inside the ArchWiki (a wonderful source of reliable information).
After tweaking the snippet a bit, I added it to ~/.config/gtk-3.0/gtk.css, like this:

.header-bar.default-decoration {
    padding-top: 1px;
    padding-bottom: 1px;
    font-size: 0.5em;
}

.header-bar.default-decoration .button.titlebutton {
    padding-top: 1px;
    padding-bottom: 1px;
    border-width: 0;
}

An that's all, no plugin needed and it is useful system wide (at least for apps which don't support client side decorations).