Question about DataFrame.style

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Hello!
In the guided project of Data Analysis in Business course, I am confused about how this section of codes work. I think

helper_df = pd.DataFrame('', index=x.index, columns=x.columns)

Should create an empty DataFrame, and the function should also return an empty DataFrame (with styles added). I don’t see why the data of the input DataFrame “relations_most_used” is conserved as shown in output.
Thank you in advance

The explanation follows directly from the documentation: