Remove ugly fat bazel from gnome-terminal with multiple-tabs

After some messing around, I figured it out.

Edit /usr/share/themes/Ambiance/gtk-3.0/apps/gnome-terminal.css and add:

 TerminalWindow .notebook {
   padding: 0;
   border-width: 0;
 }

Bug found on this: https://bugs.launchpad.net/ubuntu/+source/gnome-terminal/+bug/694468

Well its a good practice in general not to modify the original files but override their values according to your preferences.

If you don't already have it, create or open a gtk.css file in this path

~/.config/gtk-3.0/gtk.css

Paste the following code, close all terminals and start one new.

@define-color bg-grey #222;
@define-color active-grey #333;
@define-color border-grey #555;


TerminalWindow .notebook {
  border: 0;
  padding: 0;
  color: #eee;
  background-color: shade(@active-grey, 1);
}

TerminalWindow .notebook tab:active {
  border: 1px solid @border-grey;
  background-color: shade(@active-grey, 1);
}

TerminalWindow .notebook tab {
  background-color: shade(@bg-grey, 1);
}

Now, not only it will remove the borders as you intended but will also "fit" better with the dark background, my eyes "hurt" with the light gray. The result when you have multiple tabs it should look like this, which of course you can customize it by tampering the color variables according to your preferences.

Mine based on @topless and @jibreel answers.
Transparent background and a dark theme. Awesome.

@define-color bg-grey #222;
@define-color active #313131;

TerminalWindow .notebook {
    border: 0;
    padding: 0;
    color: #fff;
    background-color: shade(@active, 1);
}

TerminalWindow .notebook tab:active {
    background-color: shade(@active,1);
}

TerminalWindow .notebook tab {
    border-radius: 0px;
    padding: 3px;
    background-color: shade(@bg-grey, 1);
}