I’m not sure exactly how you want it to look, but if you add background-size: cover;
that will make the image a little more responsive (line 1159 in your css) –
.slider-wide {
background-size: cover;
background: url('http://www.lagboltmedia.com/wp-content/uploads/2013/12/skyscraper.jpg') no-repeat fixed center;
clear: both;
height: 500px;
width: 100%;
}<!--formatted-->
Then I’d remove the height that you added, but you could do that in your responsive section of the css if you want to keep it for desktop browsers.
You could also remove the margin-bottom for the .slider-wide .wrap
on 1167 in your css to remove the blue color from showing up at the bottom.