Just realized this after testing the changes I made for MAGNOLIA-4402 (these changes have nothing to do with the issue being reported here which has been verified on current demoauthor.magnolia-cms.com 4.5.2). See attached screenshot. Just for the records, on IE8 and 9 it looks fine. Since we're probably going to need different workarounds for different browsers I think it's wise to start having a look at GWT's conditional css so that also css, like javascript, is evaluated at compiled-time and a specific version for each browser is produced. One could then write something like, ie

@if user.agent ie7 {
  .myClass {
    //do horrible workarounds
  }
} @else {
  .myClass {
    //do it right
  }
}