Error installing extensions

Hi everyone,

 

I got this error when installing an extension. Can anyone help?

$ php -f bin/magento setup:static-content:deploy -f

The contents from the "/var/www/htdocs/magenton7/pub/static/frontend/Magento/luma/en_US/mage/calendar.css" file can  
  't be read. Warning!file_get_contents(/var/www/htdocs/magenton7/pub/static/frontend/Magento/luma/en_US/mage/calenda  
  r.css): failed to open stream: No such file or directory   

I see the calendar.css in the folder.