Content Width Increase?

How can I widen the content section without affecting the mobile site? Last time you guys gave me a CSS code to fix this, it worked I just believe it broke my mobile site (if I remember correctly). So unfortunately I couldn't use that code, however I really liked what it did The website is losangeleswebdesignseo dot com Another problem I am noticing is that the mobile version has a black background. Also there's a sideways looking tiny envelope in the top left corner of my mobile site. Not sure why that is happening? Basically I would really like the images to show up larger than they are on the samples page but because the content section is not wide enough the images aren't able to be as large as I'd like. Thank you