.wrap formatting

If I want to make the wrap a background-image that goes the entire width of the screen, but yet is responsive to resized browser windows and mobile how do I do that?

I created an image at 1903×350, and placed it as #wrap background-image. I added a width: 100%. I tried different “position:abc”. No dice.

I also tried to do the same in “head-wrap.” All the same issues, and it also truncated the 350px height image at 142px. Is there a way to change the 142 limitation?

More importantly, whichever area I use, how do I do so and have it render properly in resized windows and on mobile?

Thank you!