I think the keyword you wanted was 'Animated page turn' (as opposed to Flow mode)?
Don't use it (or 2 column view). just preview in single column (800x600) mode like my devices use. But I can answer the other.
Calibre 4 uses a new UI toolkit as a building block because the old one has been unsupported for quite a while. It has issues on top of differences,
You did not say FROM what version that yo upgraded from, so I can't reall nail down your result issue

There is a 'what's new' link on the download page with 2 Tabs: Current Release and you can switch to Major changes tab
On to the CSS
WHERE did you paste it? Options:Styles? and, then you clicked OK?