I’m new to Xubuntu, 25.10 to be precise, and to be honest, I think that the stripes on edges of windows where you can click on them when you want to resize a window are really narrow. And the areas in the corners you can click on to reshape the window in two directions at once are extremely tiny.
Is there some way, perhaps somewhere in the settings or a configuration file, to make these areas larger? And if there isn’t, could someone send a message upstream to the Xfce developers asking them to make these areas larger in future releases?
If you’re however asking about windows themselves; they’re just using whatever theme file you’re using in your WM (Window Manager), the default being xfwm4 for Xfce/Xubuntu. A page that maybe helpful for that is https://wiki.xfce.org/howto/xfwm4_theme
( Neither of these links maybe exactly what you’re looking for; in both cases they’re the first option that appeared in a startpage search I did based on what I considered you may be after, but I could have misunderstood what you’re asking )
Additional later thought: I tend to rarely resize using the edges of borders of windows myself; I just get the mouse somewhat close and then resize using combination of mouse & keyboard (Alt) so it doesn’t matter if I miss the edge of window by 1-2cm; it’ll work on the closest [border] to where I’m pointing[ & inside of window].
may thus be useful; given Xubuntu/Xfce defaults to XFWM4 as its’ Window Manager. My current session is LXQt from the Lubuntu team actually; but my WM is xfwm4 here so it matches perfectly when I do login & use a Xubuntu/Xfce session (this install is a multi-desktop install)