Responsive web design (RWD) is a web design approach aimed at crafting sites to provide an optimal viewing experience—easy reading and navigation with a minimum of resizing, panning, and scrolling—across a wide range of devices (from mobile phones to desktop computer monitors). A site designed with RWD adapts the layout to the viewing environment by using fluid, proportion-based grids, flexible images,and CSS3 media queries, an extension of the @media rule. – From Wikipedia
HTML5 ePub Design Resources
Handful of useful links for interactive ePub book creation.