Discovered not long ago, the new Gin admin theme is awesome. Finally, designers have decided to give a facelift and style to the Drupal back office, unchanged for many years (the famous Seven). There was indeed Adminimal or an experimental theme, Claro, which showed the way, but Gin (which requires Claro as a base) goes further. I do not see today another back office theme to work pleasantly on Drupal. If you add the 2 ecosystem modules, Gin Login and Gin Toolbar, you switch from old-school to stylish in a few clicks.
composer require drupal/gin
