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.