SU-SWS/decanter

///
/// breakpoint-previous($name, $breakpoint-names)
///
/// The $su-grid-screens map defined in the grid variables file is used as the
/// $breakpoints argument by default.
///
/// Name of the previous breakpoint, or null if the breakpoint does not exist.
///
/// breakpoint-previous(lg, (xs: 0, sm: 576px, md: 768px, lg: 992px, xl: 1200px, 2xl: 1500px))
/// Returns "md"
///
/// @group mixin
@function breakpoint-previous($name, $breakpoints: map-keys($su-grid-screens)) {
  $n: index($breakpoints, $name);
  @if is-integer($n) and $n > 1 {
    @return if($n <= length($breakpoints), nth($breakpoints, $n - 1), null);
  }
  @else {
    @return null;
  }
}