I have a lot of trouble with eyestrain and light sensitivity. In addition to special glasses, hardware fixes, and system fixes, in LibreOffice, I reset the default font to Andika, and I edited the styles, for better readability.
If I try to create a new file in LibreOffice on Windows, the styles are a mess. Instead I copy a file from my Mac, and replace the contents, so I can use the styles from my Mac. But the styles are still a mess:

I think Heading 1-3 come from the Mac, while Header, Heading, and Heading 4 come from Windows.
What’s a good way to create a consistent and readable set of styles, and get it to work with old and new documents?
I prefer for successive headings to use the same basic font, bold, either italic or not but consistent, etc.