Theme Horse

Ok got one step further:
This is what I have used and it seems to work:

.header-image {
        position: fixed;
}
#access {
	border-top: 1px solid #EAEAEA;
	border-bottom: 1px solid #EAEAEA;
        position:fixed;
}

BUT: now the header image suddenly automatically changes….
any idea how to leave the size of the header image untouched?

Thanks!