How do colors work and how to change them?

Canapin · March 20, 2025, 11:15am

The colors are (calculated) here:

app/assets/stylesheets/common/foundation/color_transformations.scss

main

// standard color transformations, use these if possible, and add any new dark-light-diffs here
// any variables defined here can be added in theme color schemes
// all variables should have the !default flag

@use "sass:string";

// primary
$primary-very-low: dark-light-diff($primary, $secondary, 97%, -82%) !default;
$primary-low: dark-light-diff($primary, $secondary, 90%, -78%) !default;
$primary-low-mid: dark-light-diff($primary, $secondary, 70%, -45%) !default;
$primary-medium: dark-light-diff($primary, $secondary, 50%, -35%) !default;
$primary-high: dark-light-diff($primary, $secondary, 30%, -25%) !default;
$primary-very-high: dark-light-diff($primary, $secondary, 15%, -10%) !default;

// primary-numbers
$primary-50: dark-light-diff($primary, $secondary, 97%, -82%) !default;
$primary-100: dark-light-diff($primary, $secondary, 94%, -80%) !default;
$primary-200: dark-light-diff($primary, $secondary, 90%, -78%) !default;
$primary-300: dark-light-diff($primary, $secondary, 80%, -60%) !default;
$primary-400: dark-light-diff($primary, $secondary, 70%, -45%) !default;

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The CSS variables are defined here:

github.com/discourse/discourse

app/assets/stylesheets/color_definitions.scss

main

// This file maps all SCSS color variables to CSS custom properties.
// It is compiled to CSS separately from the rest of the app.
// The source variables come from color_transformations.scss and variables.scss
:root {
  color-scheme: #{schemeType()};

  --scheme-type: #{schemeType()};
  --primary: #{$primary};
  --secondary: #{$secondary};
  --tertiary: #{$tertiary};
  --quaternary: #{$quaternary};
  --header_background: #{$header_background};
  --header_primary: #{$header_primary};
  --highlight: #{$highlight};
  --danger: #{$danger};
  --success: #{$success};
  --love: #{$love};
  --d-selected: #{$selected};
  --d-hover: #{$hover};
  --always-black-rgb: 0, 0, 0;

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If you want to override let’s say --primary-medium, you can add this to your theme:

:root {
    --primary-high: red;
}

However, I don’t know how to use the color transformation functions, which need SCSS variables.

I see that @import "common/foundation/variables"; is not required as “core and theme variables are now injected before any SCSS file is compiled”, but I couldn’t have it working nonetheless. I’ll pass the mic to more knowledgeable users

Topic		Replies	Views
Referencing Discourse theme color variables in custom theme component? Support css	3	36	March 21, 2025
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How do colors work and how to change them?

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