Notice that in many of the files on this site, all objects are opaque.   When constructing a file it is very useful to be able to select objects which are hidden by other objects.   This is also very useful when you are trying to make sense of a complex geometrical construction.    However, this is less attractive in a finished file.   A way to make all objects opaque when a file is finished is to choose Edit – Select All and then uncheck the Render Object Hidden Parts box in the Style window, as shown below.