SCSS (Sass) mixin to define font-size in PX, line-height and font-smoothing and then convert it to rem (base 10)

font-size-mixin.scss

// Sets up the base 10 stuff

html { font-size: 62.5%; }

// Defaults values

$default-line-height: 1.5 !default;
$default-font-smoothing: subpixel-antialiased !default;

// Function to convert pixels to rems

@function px-to-rem($size) {
    @return ($size / 10) + rem;
}

// Mixin

@mixin font-size($fs: false, $lh: $default-line-height, $sm: $default-font-smoothing ) {
   @if $fs {
        font-size: $fs  + px;
        font-size: px-to-rem($fs);
    }
    @if $lh { line-height: $lh; }
    @if $sm { -webkit-font-smoothing: $sm; }
}
// Use

@include font-size($fs: 14px, $sm: subpixel-antialiased, $lh: 1.5);