why dla ciebie does not good instead of ci?
ciebie is genitive/long-form accusative
ci is short-form dative
Oferować + sb (in dative)+ something (in accusative).
But maybe something wrong was reported and accepted.
You need to use the dative case because the job is being offered to someone.
It might be acceptable in Białystok dialect perhaps, but it's an error everywhere else, including standard.