Add body classes to your theme:
{# Edit the file mijnthema.theme #}
{# WITHIN the function musethema_preprocess_html(&$variables), add these lines #}
// Nordic: get language global variables
$language = \Drupal::languageManager()->getCurrentLanguage()->getId();
$variables['language'] = $language;
{# Add this code to the file html.html.twig #}
{# This declaration comes before the <!DOCTYPE html> line: #}
{%
set body_classes = [
logged_in ? 'user-logged-in',
not root_path ? 'path-frontpage' : 'path-' ~ root_path|clean_class,
node_type ? 'page-node-type-' ~ node_type|clean_class,
language ? 'lang-' ~ language|clean_class,
db_offline ? 'db-offline',
page.sidebar_first ? 'sidebar-first',
page.sidebar_second ? 'sidebar-second',
]
%}
{# This replaces the <body> tag: #}
<body{{ attributes.addClass(body_classes) }}>