Who pays the HOA transfer fee in California?

Can you clarify for me, who exactly is responsible for covering the HOA transfer fee in the state of California? Is it the buyer, the seller, or does it depend on the specific terms of the home sale agreement? I'm interested in understanding the general rule of thumb, as well as any potential exceptions that might apply. Additionally, is there a standard fee amount or does it vary based on factors such as the property's value or location? Thank you for your help in explaining this.