It doesn’t technically make a difference, but if you’re planning to make many changes, it’ll probably be easier to stay organized if you actually put them in a file like
custom.css. Also, this way, your Child theme will actually be a directory of files that you can backup/restore, move to another site, etc. If you put your CSS in the “Custom CSS” box then you’re just storing the styles in your WordPress database along with the rest of your Theme Options.
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