wagtail/client/scss/tools/_functions.breakpoints.scss

// Based upon the fine work and thoughts from Bootstrap v4.
//
// Copyright 2011-2018 The Bootstrap Authors
// Copyright 2011-2018 Twitter, Inc.
// Licensed under MIT (https://github.com/twbs/bootstrap/blob/master/LICENSE)

// Name of the next breakpoint, or null for the last breakpoint.
//
//    >> breakpoint-next(sm)
//    md
@function breakpoint-next($name) {
    $breakpoint-names: map-keys($breakpoints);
    $n: index($breakpoint-names, $name);
    @return if($n < length($breakpoint-names), nth($breakpoint-names, $n + 1), null);
}

// Minimum breakpoint width. Null for the smallest (first) breakpoint.
//
//    >> breakpoint-min(sm)
//    50em
@function breakpoint-min($name) {
    $min: map-get($breakpoints, $name);
    @return if($min != 0, $min, null);
}

// Maximum breakpoint width. Null for the largest (last) breakpoint.
//
//    >> breakpoint-max(sm)
//    56.1875em
@function breakpoint-max($name) {
    $next: breakpoint-next($name);
    @return if($next, breakpoint-min($next) - 0.0625em, null);
}