GNOME 3.16 remove bottom border on title bars + flat close button

before

after

Run this command:

touch ~/.config/gtk-3.0/gtk.css && echo ".ssd .titlebar {border-width: 0;box-shadow: none;}.ssd .titlebar .button.close:not(:hover):not(:active) { border-width: 0;background-image: none;box-shadow: none;}" > ~/.config/gtk-3.0/gtk.css && gnome-shell --replace

OR manually create gtk.css in ~/.config/gtk-3.0/ folder and paste following styles

/* No line below the title bar */
.ssd .titlebar {
    border-width: 0;
    box-shadow: none;
}

/* Flat close button */
.ssd .titlebar .button.close:not(:hover):not(:active) {
    border-width: 0;
    background-image: none;
    box-shadow: none;
}
then restart gnome shell with gnome-shell --replace