Bold, italic, monospace and fullwidth are Unicode letters, not a font. A field that accepts only ASCII shows the original characters. Italic βhβ uses the symbol β.
Questions
Does this change the site font?
No. These are other characters. A paste shows the shape when the app has those letters.
Do digits change too?
In styles that have Unicode digits, yes. In italic, digits stay plain.
Can I copy one style?
Select the line. The letters are Unicode and paste into another app.