You can't export HTML and CSS from Reflow at the moment. From the Adobe Edge Reflow FAQ:
Does Edge Reflow provide HTML export features?
No, but you can preview HTML designs in web browsers and experience
the responsive behaviors in end-user environments.
While Edge Reflow creates HTML during the design process, the tool is
focused on enabling designers to share their responsive design intent
and for CSS to be extracted for use either by the designer or a
developer as part of the website production process.
Edge Reflow is a prototyping tool at the moment, not a WYSIWYG web design tool that provides friendly HTML export. Adobe intend you to use it as a bridge between Photoshop and hand-coding:
- Create art assets in Photoshop.
- Mock up your design in Edge Reflow using a real browser rendering engine.
- Hand-code the design yourself. Copy CSS by clicking each container in Reflow's navigation bar at the bottom of the screen if you need to:
That's about as good as you'll get at the moment. Is is a 'preview' app, though, so it's early days.