Graphical html/css generation tool based on Google Web Toolkit (GWT)

Please make sure to read the attachment that details what technologies to use, and do not make proposals until having fully read it. We need a web-based html/css generation tool that will allow people to play around (drag - drop, resize, modify appearence) with a simple layered view in order to position html elements and pictures. The purpose of this tool is to show the user what they would see during an augmented reality experience (the tool itself will not contain any AR code, it's just like a preview). When the user is finished with his/her template, the tool should be able to generate html and css files, to be able to upload to our backend services. We will be integrating the tool into our own software, and have specific requirements with regards to the technology use. A single page working web application without the backend functionality is needed as output.