Can't get region background image to stretch 100%

On the home page I have a region containing Our Hours. There is a background image of orange/black that is set to Full Width, but there is a white line displaying above and below it. I can't figure out how to get rid of it.

I can see in the CSS that the region element is set to background-size: 1377px 124px; which is smaller than the original image, and when I edit this amount in dev mode of FireFox to make it larger by a couple of pixels, then I can get rid of the white lines. But I cannot get CSS to override the element styling. How can I change this?