Does staking ETH involve a fee?

Two days ago I bought some ETH on Binance. Yesterday I chose to stake 0.1 ETH, and correctly received 0.1 BETH in exchange. However, I noticed that my wallet instantaneously lost 30€. I thought that this was related to market fluctuations, altough the ETH price was roughly the same. Today I staked another 0.1 ETH, and again my wallet shows -30€.

So the question follows: are there fees on staking ETH? If so, what is the amount? I couldn't find anything on Binance about that.

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Thanks in advance.