I agree with everything here except for: > the common approach to dealing with breakpoints (device width) is to assume certain width parameters and build media

I agree with everything here except for: > the common approach to dealing with breakpoints (device width) is to assume certain width parameters and build media queries around that. I am opposed to targeting a fixed list of breakpoints. Instead, build the site to work at the very smallest screen size (probably vertical phone). Then, increase the size of the browser window until the site “breaks”. Note the width and set a breakpoint. Adjust the css to fit that size. Repeat until it works at the largest size. Typically this will only require two media queries.