Your question is unclear if you are asking about styling the link text created by the (click-append) macro or the resulting text after the link has been clicked.
If you mean the link text then this comment in the Harlowe -Changing color of text when hovering over a link... thread explains which CSS selectors are used by Harlowe to represent the standard normal, hover, and visited link states.
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If you mean the link text then this comment in the Harlowe -Changing color of text when hovering over a link... thread explains which CSS selectors are used by Harlowe to represent the standard normal, hover, and visited link states.