“あなたは” (anata wa): “You” with the topic marker “wa”. This shows that the sentence is about what “you” can do.
“好きなだけ” (suki na dake): “as much as you like”. “Suki” translates to “like”, and “dake” is used to mean “only” or “just”. When used together in this context, it implies “as much as you like” or “as you wish”.
“ここに” (koko ni): “here”. “Koko” translates to “here”, and “ni” is a direction or destination particle which, in this context, means “to”.
“いても良い” (itemo ii): “it is okay to be”. “Ite” is the te-form of “iru” which means “to be”, “mo” is a particle that can mean “even if”, and “ii” translates to “good” or “okay”. So “itemo ii” generally means “it’s okay to be”.
So the sentence “あなたは好きなだけここにいても良い。” translates to “You can stay here as long as you like.” It’s a kind and open-ended offer, giving the person addressed the freedom to remain in a place for a duration of their choosing.