GNOME 3: Tweak for thinner window title bars (~/.config/gtk-3.0/gtk.css)

gtk.css

window.ssd headerbar.titlebar {
    min-height: 0;
    padding-top: 1.4px;
    padding-bottom: 1.4px;
    padding-left:10px;
    padding-right:10px;
}

window.ssd headerbar.titlebar button.titlebutton {
    min-height: 0;
    padding-top: 1px;
    padding-bottom: 1px;
    min-width: 2px;
    
}

headerbar.titlebar button.titlebutton {
    margin: 4px 0px 4px 0px;
}

headerbar.titlebar {
    padding-left:8px;
    padding-right:8px;
}

headerbar {
    min-height: 38px;
    padding: 4px 10px 4px 10px
}

headerbar entry, headerbar spinbutton, headerbar button, headerbar separator {
    margin-top: 1.5px;
    margin-bottom: 1.5px;
    min-width:2px;
}

.default-decoration {
    min-height: 0;
    padding: 0.5px
}

.default-decoration .titlebutton {
    min-height: 10px;
    min-width: 10px; 
}