//下一个断点
@function breakpoint-next(
  $name,
  $breakpoints: breakpoints,
  $breakpoint-names: map-keys($breakpoints)
) {
  $n: index($breakpoint-names, $name);
  @return if(
    $n < length($breakpoint-names),
    nth($breakpoint-names, $n + 1),
    null
  );
}

//断点最小值
@function breakpoint-min($name, $breakpoints: $breakpoints) {
  $min: map-get($breakpoints, $name); // @return if($min != 0, $min, null);
  @return $min;
}

//断点最大值
@function breakpoint-max($name, $breakpoints: $breakpoints) {
  $next: breakpoint-next($name, $breakpoints);
  @return if($next, breakpoint-min($next, $breakpoints) - 1px, null);
}

//生成类名“-sm、-md、-lg、-cl” -xs?
@function breakpoint-infix($name, $breakpoints: $breakpoints) {
  @return if(breakpoint-min($name, $breakpoints) ==null, '', '-#{$name}');
}

@function px2rem($pixels, $context: $remFactor) {
  @if (unitless($pixels)) {
    $pixels: $pixels * 1px;
  }

  @if (unitless($context)) {
    $context: $context * 1px;
  }

  @return $pixels / $context * 1rem;
}