Thanks Ciarán,
#breadcrumb {
padding-top: 5px !important;
}
doesn't work to amend the white space above the breadcrumb, it only made the breadcrumb stick close to the menue. I figured out, that the white space ist exactly as high as the menu, so after menu breackpoint the menu disappears and instead the white space appears. It has also something to do with the #undefined-sticky-wrapper, but I cant't find out how to fix it. Would be great if you had another look. Thanks for help!!!
I changed all images from .png to .jpg (except the logos). Thanks for that hint!
Tanja