[Theme: Pinboard] – changing header color and image

Hello,

I am quite new to WordPress and CSS and I am trying to essentially have the header have a black background with my logo centered in the middle; however, I was unable to change the background color of the header without changing the background color of the entire website. Instead I have just created a .jpeg with my logo on a black background and I would like it to cover the entire header. Are there certain dimensions that I should up the image to or is there an easier way to do this?

Also, my twitter, pinterest and search icons appear below the header image. Is there a way to get them to hover above the image on the black background?

I think the easiest fix, if possible, is to change just the header color. If this is not possible I need to know how to get the icons to hover and which dimensions my image needs.

The website is chicthestyle.com

Thank you in advance for any help,

Dustin