I want to customize the maintenance page in Drupal 8.
How do I theme it?
In Drupal 8, settings.php contains the following line:
# $settings['maintenance_theme'] = 'bartik';
First, uncomment this setting and change "bartik" to the machine name of your custom theme.
Next, copy the core maintenance template core/modules/system/templates/maintenance-page.html.twig to templates/maintenance-page.html.twig in your custom theme directory.