What I can do is move them into the <style> tag above where the rest of the CSS is, that's  where they belong.

As far is what each one does:
"overflow: visible;" removes the extra vertical scrollbar.  Without this the browser's vertical scroll bar renders with very little scrollable space and another vertical scroll bar renders inside the document, around the notebook contents, which handles the scrolling of the document.
"border-top: none;" removes a small 1px grey border from the top of the notebook
shadow stuff- removes a very faint shadow that surrounds the whole document