Sorry for being such a php/html/css-moron…
At least I succeeded in activating the snippet (Thanks, Lyle!).
Considering the menu (set “below header”):
It disappeared from the header, alright. It did not appear above the footer-bar, though.
I scrolled down all the blogs an found out that – on the very last moment before hitting the bottom of the blog-roll – the search-button-magnifier-glass from my initial header scrolls into the footer-bar from the bottom of my screen.