Separate header from content and remove header background

Install this Custom CSS Manager plugin http://wordpress.org/plugins/custom-css-manager-plugin

Then use its section of the dashboard to hold your CSS modifications:

#page,
#access {
 background: none;
}

#branding {
 border: 0;
}

#access {
 -webkit-box-shadow: none;
 box-shadow: none;
}

#main {
 background: #fff;
 overflow: hidden;
}