Ah - so you're seeing something similar to this:
If you go back to the first post in this topic, you'll see that as the resolution gets wider with this theme, more of the background image shows. The background is designed so that all of it isn't seen unless someone is using a resolution of 1680X945. That's a bit too big for me - even on my big screen TV - but some people do like it. And if anyone goes with an even wider resolution, the background image will even begin to repeat, though it will remain centered. Here's an example at 1920X1080:
One thing to remember with a widescreen monitor, though, is that certain resolutions actually distort their display somewhat. A widescreen monitor is designed for aspect ratios of 16:9, which is decimally represented as 1.7777777. 1366X768 is very close to that (1.7786758) - but resolutions of, say, 1152X648, 1280X720, 1680X945 or 1920X1080 are exact. It all depends on personal preference and whether someone tolerates distortion. For example, a 4:3 aspect ratio (1.3333333), which is designed for a normal monitor and/or TV, is not at all good on a widescreen monitor/TV. Here's an example of 1280X960:
YUK - images and text are stretched out! The correct display (at 1280X720) looks like this: