$breakpoints: (
                    "palm"          "screen and (max-width: 44.9375em)",
                    "lap"           "screen and (min-width: 45em) and (max-width: 63.9375em)",
                    "lap-and-up"    "screen and (min-width: 45em)",
                    "portable"      "screen and (max-width: 63.9375em)",
                    "desk"          "screen and (min-width: 64em)",
                    "retina"        "(-webkit-min-device-pixel-ratio: 2), (min-resolution: 192dpi)"
                ) !default;
                

You can change these values to your needs and add more to the list if you lack any breakpoint by copying this whole list into your css and add your changes.