The Nodes Gallery (usr/share/data/vrml) contains two Background nodes that you can add to your scene. The files are
Add the background to your scene either by dragging and dropping the file icon from the desktop or by using the File > Import menu. (Note: you may receive a warning message, but you can ignore it and continue.)
Currently, you can't change the number of ground angles or sky angles in the Background node, but you can modify their values in the Outline Editor. To change the number of angles, edit the original file containing the Background node before you import it into your scene.