decrease the size of gnome terminal / gtk3 window title and window tabs

gtk.css

/* Decrease the tabs bar height in gnome-terminal
 * Add: ~/.config/gtk-3.0/gtk.css
 * See: https://stackoverflow.com/questions/36869701/decrease-the-tabs-bar-height-in-gnome-terminal
 */

terminal-window notebook > header.top button {
  padding: 0 0 0 0;
  background-image: none;
  border: 0;
  margin-right: 10px;
  font-size: 10px;
}
terminal-window notebook > header.top > tabs > tab {
  margin: 0 0 0 0;
  padding: 0 0 0 0;
  font-size: 10px;
}
terminal-window notebook > header.top > tabs > tab label {
  padding: 0 0 0 0;
  margin: 0 0 0 0;
  font-size: 10px;
}

/* shrink headerbars (don't forget semicolons after each property) */
headerbar {
    min-height: 0px;
    padding-left: 2px; /* same as childrens vertical margins for nicer proportions */
    padding-right: 2px;
    background-color: #2d2d2d;
    font-size: 10px;
}

headerbar entry,
headerbar spinbutton,
headerbar button,
headerbar separator {
    margin-top: 0px; /* same as headerbar side padding for nicer proportions */
    margin-bottom: 0px;
}

/* shrink ssd titlebars */
.default-decoration {
    min-height: 0; /* let the entry and button drive the titlebar size */
    padding: 0px;
    background-color: #2d2d2d;
}

.default-decoration .titlebutton {
    min-height: 0px; /* tweak these two props to reduce button size */
    min-width: 0px;
}

window.ssd headerbar.titlebar {
    padding-top: 0;
    padding-bottom: 0;
    min-height: 0;
}