Decreased background size in Tenebris theme.

System version 0.344
modules:
Blogs 0.061
Comments 0.019
Cron 0.008
Feedback 0.005
HybridAuth 2.1.1-cs27
OAuth2 0.025
Photo_gallery 0.014
Plupload 1.5.7-cs10
Static_pages 0.036
plugins:
Admin_default_theme 0.005
Fotorama 4.4.3-cs1
SimpleImage 2.3-cs1
TinyMCE 4.0.6-cs1