Generated by SassMeister.com.

SassMeister-input.scss

// ----
// libsass (v3.2.5)
// ----

$sizePx: 18px;
$basePx: 16px;
$unit--rem: true;

// CHECK BOOLEAN VALUE
@function bool($value: false) {
    @if $value == false or 
        $value == "" or 
        $value == "false" or 
        $value == 'false' or 
        $value == 0 {
            @return false;
        }
    @return true;
}

// Converts PX to REM based on base font size
@function rem($sizePx, $baseFontSizePx) {
    @return ($sizePx / $baseFontSizePx) * 1rem;
}

// Font size mixin
@mixin font-size($sizePx, $basePx, $important: false) {
    @if bool($important) == false {
        font-size: round($sizePx);
        @if bool($unit--rem) == true { font-size: rem($sizePx, $basePx); }
    }
    @else {
        font-size: round($sizePx) !important;
        @if bool($unit--rem) == true { font-size: rem($sizePx, $basePx) !important; }       
    }
}

// Test
.test {
  @include font-size($sizePx, $basePx, true);
}

SassMeister-output.css

.test {
  font-size: 18px !important;
  font-size: 1.125rem !important;
}