Due to the very nature of CSD itself, CSD apps often don’t respect desktop themes. It also, unless designed to compensate, oftentimes does not provide proper context menus due to its use of popover menus.
Not as much of a problem on phones or tablets as unified themes across apps aren’t really used as often on those platforms, but it’s a problem that happens a lot on desktop, for example on GNOME.
A lot of it comes down to the fact that many CSD apps, due to how CSD itself works, don’t respect desktop themes such as that which GNOME has, and due to using popover menus as opposed to traditional menus also don’t provide proper context menus.