http://kuukkanen.i2p/posts/ui-toolkits
Linux,
unlike Windows or macOS, doesn’t have a “native” toolkit or UI style to follow.
Some desktop environments, like GNOME and KDE Plasma, have their own style and
applications made for those desktops look great, but reality isn’t quite that
simple. Linux is a mixed bag of different applications, desktop environments,
window managers, and UI styles, so it’s not exactly easy to create a concise and
coherent look...