$headings: h1 3rem 900, h2 1.6rem 700, h3 1.3rem 600, h4 1.2rem 400,
  h5 1.1rem 300, h6 1rem 100;

@mixin setHeading {
  @each $name, $size, $weight in $headings {
    .#{$name} {
      font-size: $size;
      font-weight: $weight;
    }
  }
}

@include setHeading();

body {
  font-family: system-ui, -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto,
    Oxygen, Ubuntu, Cantarell, "Open Sans", "Helvetica Neue", sans-serif;
}