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Theming Guidelines


We’re currently making rapid changes to the product so our docs may be out of date. If you need help, please email

Forem supports different themes, such as Default, Night, Pink.

You can switch the theme at http://localhost:3000/settings/ux in the "Style Customization" section.

These themes are powered by CSS custom properties, loaded at runtime by JavaScript via layouts/_user_config.html.erb.

An example of how it works:

try {
const bodyClass = localStorage.getItem('config_body_class');

if (bodyClass) {
document.body.className = bodyClass;

if (bodyClass.includes('night-theme')) {
document.getElementById('body-styles').innerHTML = '<style><%= Rails.application.assets["themes/night.css"].to_s.squish.html_safe %></style>';
} else if (bodyClass.includes('ten-x-hacker-theme')) {
document.getElementById('body-styles').innerHTML = '<style><%= Rails.application.assets["themes/hacker.css"].to_s.squish.html_safe %></style>'
} else if (bodyClass.includes('pink-theme')) {
document.getElementById('body-styles').innerHTML = '<style><%= Rails.application.assets["themes/pink.css"].to_s.squish.html_safe %></style>'
} else if(bodyClass.includes('minimal-light-theme')) {
document.getElementById('body-styles').innerHTML = '<style><%= Rails.application.assets["themes/minimal.css"].to_s.squish.html_safe %></style>'

Within SCSS files located at app/assets/stylesheets you can use var() statements, which will call these CSS custom properties. If a CSS custom property is not defined var() will fall back on the second parameter provided, which can be a SCSS variable defined in app/assets/stylesheets/variables.scss.

An example of how to use var():

div {
color: var(--theme-color, $black);

Note that fallback values aren't used to fix the browser compatibility. If the browser doesn't support CSS custom Properties, the fallback value won't help. To prevent this issue on older browsers, we need to write our styles like this:

div {
color: $black;
color: var(--theme-color, $black);

This can be too much work and browser fallback can be forgotten. For a better developer experience, you should use the two mixins defined in app/assets/stylesheets/_mixins.scss called themeable and themeable-important. They take three arguments. The first argument is the CSS property like color or background, the second argument is the CSS custom property name (without --) like theme-color, and the third argument is the CSS value, i.e., $black or white.

Make sure to import the mixin in your SCSS file and use it like this:

div {
@include themeable(color, theme-color, $black);

themeable-important is used when a CSS variable requires !important as a postfix of the CSS property's value where the CSS variable is being used. You can use it the same way you would use themeable mixin, but you should avoid !important if possible.

Other user config

In addition to themes, users can also directly configure their preferred fonts and their nav bar preferences. The implementation of these is similar to themes.