Você pode usar o seguinte estilo para fazer a guia funcionar:
/* gnome-terminal */
@define-color terminal_bg #300a24;
@define-color bg_color_active_tab #157bb7;
notebook.terminal-notebook header.top tab,
notebook.terminal-notebook header.top tab:hover {
background-image: -gtk-gradient (linear, left top, left bottom,
from (shade (@fg_color, 0.92)),
color-stop (0.60, shade (@fg_color, 0.9)),
to (shade (@fg_color, 0.85)));
color: @bg_color;
}
notebook.terminal-notebook header.top tab:checked {
background-image: -gtk-gradient (linear, left top, left bottom,
from (shade (@bg_color_active_tab, 1.2)),
to (shade (@bg_color_active_tab, 1.12)));
color: @bg_color;
}
Isso resultará em: