Load additional stylesheets in TYPO3 backend

[zenoussi]

It is possible to load additional CSS files for the TYPO3 backend interface via regular $TYPO3_CONF_VARS settings in a settings.php file of a project (previously known as LocalConfiguration.php) file or in an extension's ext_localconf.php.

$GLOBALS['TYPO3_CONF_VARS']['BE']['stylesheets'][my_extension] = 'EXT:myextension/Resources/Public/Css/myfile.css';
$GLOBALS['TYPO3_CONF_VARS']['BE']['stylesheets'][my_extension] = 'EXT:myextension/Resources/Public/Css/';

How can the requirements be solved?

Thanks a lot