A site designed with RWD adapts the layout to the viewing environment by using fluid, proportion-based grids, flexible images,and CSS3 media queries. Many modern WordPress themes come 'out of the box' built to be responsive.
MemberMouse core pages come equipped with useful SmartTags to help create an easy way for your membership site to function. These core pages also come with a specific CSS stylesheet that allows you unparalleled control over the look of these pages
With MM version 2.2.0 or higher, the checkout page has been developed to be responsive. Just make sure that if you had installed MM prior to 2.2.0 that you pull down the latest checkout core page template.