If you want any chance of a Linux app looking at all "native" to the user's currently selected theme, your best bet is to let the window manager draw the window

If you want any chance of a Linux app looking at all "native" to the user's currently selected theme, your best bet is to let the window manager draw the window frame, which includes the title bar and minimize/close buttons. Chrome specifically doesn't try to look native in its default state, but also gives the user the option to let the window manager draw the window frame, to fit in at the expense of using more space overall. This is a side effect of X11 and window manager APIs, as well as the proliferation of competing window managers and widget toolkits like Qt, Gtk, etc.