How to change gedit's active tab color to make easy to verify current tab.

For Ambiance theme, find gtk-widgets.css for Ambiance theme.

mine is in below directory,
/usr/share/themes/Ambiance/gtk-3.0/gtk-widgets.css

edit the file with root permission.

~$ sudo gedit /usr/share/themes/Ambiance/gtk-3.0/gtk-widgets.css


find below line from the file.

/* give active tab a background, as it might be dragged across of others when reordering */
.notebook tab:active {
    background-color: @bg_color;
}


change color to something else, for me I put some shade so active tab will be darker than others.

/* give active tab a background, as it might be dragged across of others when reordering */
.notebook tab:active {
    background-color: shade (@bg_color, 0.82);
}