Breakpoint settings file contains a list of the breakpoint sizes.
npm install --save iotacss-breakpoint
$iota-breakpoint-sizes : (
sm : "screen and ( min-width: 768px )",
smo : "screen and (min-width: 768px ) and (max-width: 999px )",
md : "screen and ( min-width: 1000px )"
) !default;