Remove old VimFxFindInput CSS
Cleanup CSS a bit
Raise the z-indexes used to trump youtube

Youtube uses 1999999999 as z-index for its top bar, which is a lot
higher than VimFx used for the help dialog and markers. This caused the
top bar to overlap the help dialog, and, more importantly, the markers,
making it impossible to see the marker for the search box, for example.

This commit raises VimFx’s z-indexes to trump Youtube.