Several crittical bugfixes and improvements

I used REM-unit-polyfill in our project and found several critical errors. 

Also I fixed original font size calculation (see comment to commit) - I think that there is no other possibility than change body font size for calculation and restoring after it (at least I didn't find). But without this rem calculates wrong.

Notice: I didn't change minified version - please, do it by yourself. Thanks