After some hours of searching and playing with various tags and even a MSIE/other browser selector the result is what she expected and even visible for all sorts of browsers. My own site is only slightly changed, no change of theme, just an upgrade. To be ‘more compatible’ with wordpress I moved my language switcher to a widget.
The new Mandigo-thema is capable of ‘trimming’ the header image to ‘just 100px’, that looks a lot smarter than before (the large beam) and … the colors are kept! Inline with Marianne’s website i’m also using the picturegallery two and activated the lightbox part for some of the newer posts.
So, if you are looking how I defeated the CSS trouble, just check Marianne’s website. The stylesheets (ending in MSIE or other).