RapidWeaver Stacks add-on info:
Working with responsive websigen you must define what happens when user browses your site on a smaller website. On a computer screen you can easily have 4-5-6 columns side by side, but only on on a smartphone.
The Responsive MaxWidth Stack allows you to define up to 3 breakpoints: How padding are defined for each breakpoint and what max-width to break to. There's (as most of my Stacks have) an option to add custom css for each breakpoint. Maybe you want a different background at a certain breakpoint or different text color.
RapidWeaver, stacks, responsive, free stack.