There are a few built-in window styles in X-Plane that you can use.

Note that X-Plane 6 does not offer real shadow-compositing; you must make sure to put a window on top of another window of the right style to the shadows work, etc. This applies to elements with insets and shadows. The rules are:

Sub windows must go on top of main windows, and screens and list views on top of subwindows. Only help and main windows can be over the main screen.

With X-Plane 7 any window or element may be placed over any other element.

Some windows are scaled by stretching, some by repeating. The drawing routines know which scaling method to use. The list view cannot be rescaled in X-Plane 6 because it has both a repeating pattern and a gradient in one element. All other elements can be rescaled.

xpWindow_Help"0" An LCD screen that shows help.
xpWindow_MainWindow"1" A dialog box window.
xpWindow_SubWindow"2" A panel or frame within a dialog box window.
xpWindow_Screen"4" An LCD screen within a panel to hold text displays.
xpWindow_ListView"5" A list view within a panel for scrolling file names, etc.