mastodon/app/views/custom_css/show.css.erb

<%- if Setting.custom_css.present? %>
<%= raw Setting.custom_css %>

<%- end %>
<%- UserRole.where(highlighted: true).select { |role| role.color.present? }.each do |role| %>
.user-role-<%= role.id %> {
  --user-role-accent: <%= role.color %>;
}

<%- end %>