The document discusses using Sass mixins to generate responsive breakpoints and media queries. It shows how to:
1. Create responsive breakpoints and styles for different screen widths using Sass mixins that generate the appropriate CSS media queries.
2. Target high resolution displays by generating different background images for retina and non-retina screens.
3. Fall back to styles without media queries for older browsers by passing different parameters to the breakpoint mixins or setting variables before importing partial Sass files.