discourse/app/assets/stylesheets/common/foundation/variables.scss

// --------------------------------------------------
// Variables used throughout the theme
// --------------------------------------------------

// Layout dimensions
// --------------------------------------------------

$small-width: 800px !default;
$medium-width: 995px !default;
$large-width: 1110px !default;

// Brand color variables
// --------------------------------------------------

$google: #5b76f7 !default;
$facebook: #3b5998 !default;
$cas: #70BA61 !default;
$twitter: #00bced !default;
$yahoo: #810293 !default;
$github: #6d6d6d !default;

// Fonts
// --------------------------------------------------

$base-font-size: 14px !default;
$base-line-height: 19px !default;
$base-font-family: Helvetica, Arial, sans-serif !default;

/* These files don't actually exist. They're injected by DiscourseSassImporter. */
@import "theme_variables";
@import "plugins_variables";

// w3c definition of color brightness
@function brightness($color) {
  @return ((red($color) * .299) + (green($color) * .587) + (blue($color) * .114));
}

@function dark-light-diff($adjusted-color, $comparison-color, $lightness, $darkness) {
  @if brightness($adjusted-color) < brightness($comparison-color) {
    @return scale-color($adjusted-color, $lightness: $lightness);
  } @else {
    @return scale-color($adjusted-color, $lightness: $darkness);
  }
}
@function dark-light-choose($light-theme-result, $dark-theme-result) {
  @if brightness($primary) < brightness($secondary) {
    @return $light-theme-result;
  } @else {
    @return $dark-theme-result;
  }
}