Sass mixin for the headings: file #1 REM, file #2 PX

font-sizes-px.scss

$base-font-size: 16px;
$heading-scale: 6;

@for $i from 1 through 6 {
    h#{$i} {
        font-size: $base-font-size + $heading-scale * (6 - $i);
    }
}

// sizes 46px, 40px, 34px, 28px, 22px, 16px

font-sizes-rem.scss

$step-size-heading: 0.4;
$amplifier-heading: 1.25;

@mixin heading-size($size) {
    font-size: $size * $step-size-heading * $amplifier-heading + rem;
}

h1 {
    @include heading-size(6); // 3rem
}

h2 {
    @include heading-size(5); // 2.5rem
}

h3 {
    @include heading-size(4); // 2rem
}

h4 {
    @include heading-size(3); // 1.5rem
}

h5 {
    font-size: 1.25rem; // 1.25rem (if include = 1rem)
}

h6 {
    font-size: 1rem; // 1rem (if include = 0.5rem)
}