FIX_TABSIZE

In many themes notebook and tabs are way oversized for the terminator use
It has been corrected for the Clearlooks theme. If you use other theme
you need to edit css for your theme, ie. (before install) in the
  YOURTHEMEname/gtk-3.0/apps/terminator_styling.css

or (after install) in your home:
  ~/.local/share/themes/yourTHEMEname/gtk-3.0/apps/terminator_styling.css

As the Clearlooks theming is minimal, you may start wit straight copy of it:
  cd ~/.local/share/themes   # or in other distros: cd ~/.themes

  cp -r Clearlooks yourTHEMEname

Then edit css files there. Remember that  ~/.local/share/themes/yourTHEMEname
is searched first (by the GTK) and only then the newer ~/.themes directory is.

Q: how to check your theme name from the console:

A: (XFCE)  xfconf-query -c xsettings -p /Net/ThemeName
A: (GNOME) gsettings get org.gnome.desktop.interface gtk-theme