What is the stETH fee for Lido?

Could you please explain to me what the stETH fee for Lido actually entails? I'm a bit confused about the specifics. Is it a flat rate, or does it vary depending on certain conditions? Additionally, how does Lido determine this fee? Is it based on the amount of stETH I'm staking or perhaps the duration of the staking period? Also, is there a minimum or maximum fee that applies? Lastly, how often are these fees adjusted, and are there any notifications or announcements made when changes occur? Thank you for clarifying this for me.