@Josteglitz @libreoffice Hmm, for GtK3, that entails adding to ~/.config/gtk-3.0/gtk.css
scrollbar, scrollbar button, scrollbar slider {
-GtkScrollbar-has-backward-stepper: true;
-GtkScrollbar-has-forward-stepper: true;
min-width: 20px;
min-height: 20px;
border-radius: 0;
}

You would adjust min-width to whatever suits you.

It seems libreoffice uses Gtk3 for some things and GtK4 for some things (of course GtK4 has removed theming support, as why give users the freedom to adjust the software as they would like?).