How to make a button float in React using MUI?

I want to make an AppBar, and I used the to make the navigation button float, but when it shows on the browser, the Fab acts just like a button and misaligns everything else.
How to fix this?

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In the AppBar, I centered the title, but because the Fab doesn’t actually float, it takes up a space left of the title, which makes the title jumped to the left.