Why doesn't the example for the Stepper component from material-ui work?

Question

React

Good afternoon
I don’t understand why the example for the vertical Stepper from Material-Ui does not work for me. I pasted the code from their example www.material-ui.com/#/components/stepper - (see Vertical Linear Stepper), but for some reason my Step is stretching to the full height of the body.

I compared styles element by element - everything is the same. There is nothing superfluous in the code of my page - just an example.
Can anyone try this example?
Thanks in advance for your help.