Here is an example of how to use the :pane option of define-application-frame :
(define-application-frame test-frame ()
()
(:pane
(vertically ()
(make-clim-interactor-pane
:foreground +green+
:background +red+)
(make-pane 'push-button
:label "press me"
:background +black+
:foreground +purple+
:activate-callback
#'(lambda (button)
(frame-exit *application-frame*))
:text-style
(make-text-style :serif :roman 20)))))