Additionally, the installation summary page looks different than usual, it does not load styles and other elements

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Pre-installation verification
The installer has performed a series of tests to verify that everything is ready to begin the installation process.
Checking PHP version: OK!
Checking if the iconv extension is available: OK!
Checking if session handling is configured correctly: OK!
Checking if the /assets/cache and /assets/cache/rss folders are writable: OK!
Checking if the /assets/cache/siteCache.idx.php file is writable: OK!
Checking if the /assets/images, /assets/files, /assets/backup and /assets/.thumbs folders exist: OK!
Checking if the /assets/images, /assets/files, /assets/backup and /assets/.thumbs folders exist: OK!
Checking if the /assets/export folder exists: OK!
Checking if /assets/export folder is writable: OK!
Checking if /manager/includes/config.inc.php file exists and is writable: OK!
Connecting to database: Database connection failed!
Check your username and password, then try again.SQLSTATE[HY000] [1045] Access denied for user ''@'localhost' (using password: YES)
The database cannot be used!
Check the database permissions for the selected user, and then try again.