У вашего броузера проблема в совместимости с HTML5
One of the really nifty additions to Dreamweaver CS6 is Fluid Grids. If you are just starting to explore the concepts of Mobile First and Responsive Design then a great place to start is the Fluid Grid Layouts because, as a visual editor, Dreamweaver lets you see what you are doing and how changes to the CSS ripple from a smartphone, across a tablet and land on the desktop. Learn more about Dreamweaver's Fluid Grids on Webdesigntuts+ http://enva.to/Pp8Q5J