Are the context menus hardcoded? Ghosttty is the only app on my machine that uses those horrendous rounded context menus, and because I don't use a compositor, they also have a giant black band around them. None of the config file settings seemed relevant, but maybe I missed something?
window.zig: widget.addCssClass("no-border-radius") when no compositor is detected seems like it should be preventing this, but it's clearly not working.