Drupal 8: Broken Web UI

Most probably caused by CSS/JS Aggreggation. Disable it by doing the following:

Can edit settings.php - add the following:

1$config['system.performance']['css']['preprocess'] = FALSE;
2$config['system.performance']['js']['preprocess'] = FALSE;

In Drupal Admin

-site-/admin/config/development/performance

Uncheck two checkboxes:

  • Aggregate CSS files
  • Aggregate JavaScript files

Reference: https://www.drupal.org/forum/support/post-installation/2017-04-02/disabling-caching-cssjs-aggregation