Changing the global font of Stewart theme

I am trying to set up my site in an FSE theme. I am a blogger (not a developer) who has very limited experience with CSS coding. I want the font to be used throughout my site to be “Lato”. Is there a way and a place to insert custom CSS that will result in propagating that font consistently throughout the entire site? I see there is a “Customize” option on the “Appearance” menu that has a place for entering “Additional CSS” and I wondered if it could be relevant to doing this. I could not find any instructions on how to use this function. I would appreciate help/guidance.

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