//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;
}