[giow] (0) Make the default styling for modal dialogs not overflow the device on small screens
Fixing https://www.w3.org/Bugs/Public/show_bug.cgi?id=24991
Affected topics: Rendering

git-svn-id: http://svn.whatwg.org/webapps@8750 340c8d12-0b0e-0410-8428-c7bf67bfef74