[SOLVED] Amending the Header height

I am trying to amend the Header height and/or insert a top margin on the header . When using firebug I can do this ok. According to firebug the file I need to edit is nexus.css. When I amend the actual file for real, nothing happens.
What am I doing wrong?

denhammedia.com/bodi

Add this syntax below to your css/csutom.css

#header {
margin-top: 200px;
}

Problem solved.