In this case though, all the elements have width explicitly specified: the sidebar & toolbar are a fixed number in px and the center content is `width: 100%`.  They all have position explicitly set as well.  So in theory what you described should never come into play.

The extreme flakiness coupled with snapping back into alignment at the slightest DOM change has all the hallmarks of a browser bug to me... which is scary.

Thankfully the alternative of using (left, right) rather than (width: 100%, padding-left, padding-right) doesn't seem to have this problem, and the code is cleaner to boot... so I'll put up a commit that uses that approach instead.  (Not sure why Garth chose the width: 100% route instead, but I'll ping him).