Responsive Typography with Maps From http://www.smashingmagazine.com/2015/06/responsive-typography-with-sass-maps/

SassMeister-input.scss

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

// From http://www.smashingmagazine.com/2015/06/responsive-typography-with-sass-maps/

$breakpoints: (
  small : 480px,
  medium: 700px,
  large : 1024px
) !default;

$p-font-sizes: (
  null  : (15px, 1.3),
  small : 16px,
  medium: (17px, 1.4),
  900px : 18px,
  large : (19px, 1.45),
  1440px: 20px,
) !default;


@mixin font-size($fs-map, $fs-breakpoints: $breakpoints) {
  @each $fs-breakpoint, $fs-font-size in $fs-map {
    @if $fs-breakpoint == null {
      @include make-font-size($fs-font-size);
    }
    @else {
      // If $fs-font-size is a key that exists in
      // $fs-breakpoints, use the value
      @if map-has-key($fs-breakpoints, $fs-breakpoint) {
        $fs-breakpoint: map-get($fs-breakpoints, $fs-breakpoint);
      }
      @media screen and (min-width: $fs-breakpoint) {
        @include make-font-size($fs-font-size);
      }
    }
  }
}

// Utility function for mixin font-size
@mixin make-font-size($fs-font-size) {
  // If $fs-font-size is a list, include
  // both font-size and line-height
  @if type-of($fs-font-size) == "list" {
    font-size: nth($fs-font-size, 1);
    @if (length($fs-font-size) > 1) {
      line-height: nth($fs-font-size, 2);
    }
  }
  @else {
    font-size: $fs-font-size;
  }
}

p {
  @include font-size($p-font-sizes);
}

SassMeister-output.css

p {
  font-size: 15px;
  line-height: 1.3;
}

@media screen and (min-width: 480px) {
  p {
    font-size: 16px;
  }
}

@media screen and (min-width: 700px) {
  p {
    font-size: 17px;
    line-height: 1.4;
  }
}

@media screen and (min-width: 900px) {
  p {
    font-size: 18px;
  }
}

@media screen and (min-width: 1024px) {
  p {
    font-size: 19px;
    line-height: 1.45;
  }
}

@media screen and (min-width: 1440px) {
  p {
    font-size: 20px;
  }
}