I would start by removing the link to the device specific styles.
Then I would change #wrapper as follows and rethink how I want the page to flow as the viewport becomes narrower.
#wrapper {
border: 1px solid red;
margin: 0 auto;
/* min-width: 1250px; /* DELETE Me */
/* width: 1350px; /* DELETE Me */
max-width:1350px; /* ADD Me */
}
The <header>
is a block element. Block elements extend to the full width of the available space by default. I would delete {width:100%} from any blocks that have {width:100%} assigned unnecessarily.
Fixed heights are usually poor design as they do not change height as their contents change. You my want to specify a min-height rather than a fixed height, but in this case, I’d start with no height assigned.
header {
border: solid 3px gray;
/* width: 100%; /* DELETE Me */
/* min-height: 270px; /* changed from {height:...} *//* DELETE Me */
}