1. Copy APP.php to /usr/share/zabbix/include/classes/core/APP.php
   This File adds a "Auto Theme" to the Default Theme pool by overriding the Method getThemes() from ZBase.
   If you already have a File like this simply add this Code your class APP extends ZBase

   public static function getThemes() {
       return array_merge(parent::getThemes(), [
           /* 'css_file_name_without_extension' => _('theme_name_in_ui') */
               'automatic_dark_mode' => _('Auto Theme')
       ]);
   }

2. Copy automatic_dark_mode.css to /usr/share/zabbix/assets/style/auto_dark_mode.css
   This CSS File simply imports either blue-theme.css or dark-theme.css depending on what the media query prefers-color-scheme returns. (dark/light) You can also import alternate *.css Files by simply changing url('<file>').

After you restart the Zabbix Frontend, a new Theme called Auto Theme should appear.

1. Create a Data or Provisioning Folder withing you Compose Project
   The "Source" Files will be placed in this Directory
   Only APP.php and automatic_dark_mode.css is required
2. Added Read-Only Mounts to your Docker Compose File
   

   volumes:
       - ./provisioning/zabbix/frontend/APP.php:/usr/share/zabbix/include/classes/core/APP.php:ro
       - ./provisioning/zabbix/frontend/automatic_dark_mode.css:/usr/share/zabbix/assets/styles/automatic_dark_mode.css:ro

   This will add both Files as Read-Only Mounts

This should be enough, but depending on your Docker Compose Project you might need to
complete additonal steps

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