This is a more complicated version that includes a fallback to display the map on a single page if the page aspect is landscape (or if the page aspect can't be determined.)
It seems to work okay on both Kobo readers (ACCESS-based using CSS @media queries; and Adobe RMSDK10-based using XPGT conditionals), but doesn't work in the Calibre viewer, where there is something odd going on with the results of the @media queries. It might be that I am still using Calibre 2.85 and it has been fixed in the latest version though.
default.css:
media.css:
media.xpgt:
map.html: