notes/node_modules/primer-support/lib/mixins/typography.scss

// Text hiding for image based text replacement.
// Higher performance than -9999px because it only renders
// the size of the actual text, not a full 9999px box.
@mixin hide-text() {
  overflow: hidden;
  text-indent: 100%;
  white-space: nowrap;
}

// Heading mixins for use within components
// These match heading utilities in utilities/typography
@mixin h1 {
  font-size: $h1-size;
  font-weight: $font-weight-bold;
}

@mixin h2 {
  font-size: $h2-size;
  font-weight: $font-weight-bold;
}

@mixin h3 {
  font-size: $h3-size;
  font-weight: $font-weight-bold;
}

@mixin h4 {
  font-size: $h4-size;
  font-weight: $font-weight-bold;
}

@mixin h5 {
  font-size: $h5-size;
  font-weight: $font-weight-bold;
}

@mixin h6 {
  font-size: $h6-size;
  font-weight: $font-weight-bold;
}

// Responsive heading mixins
// There are no responsive mixins for h5 and h6 because they are small
// and don't need to be smaller on mobile.
@mixin h1-reponsive {
  font-size: 26px;
  font-weight: $font-weight-bold;

  // Up to 32px in future
  @include breakpoint(md) { font-size: 30px; }

}

@mixin h2-responsive {
  font-size: 20px;
  font-weight: $font-weight-bold;

  // Up to 22px or 24px in future
  @include breakpoint(md) { font-size: 21px; }
}

@mixin h3-responsive {
  font-size: 14px;
  font-weight: $font-weight-bold;

  @include breakpoint(md) { font-size: 16px; }

}

@mixin h4-responsive {
  font-size: 13px;
  font-weight: $font-weight-bold;

  @include breakpoint(md) { font-size: 14px; }

}