At this time there is no way to style the unsubscribe link in Sitefinity 6.1. The sitefinity style classes prevent users from editing inline style rules and prevent setting the styles through a masterpage, as well. I will file this issue as a bug, since it requires further investigation on our side. You can track the status of the bug here
Please accept our apologies for the inconvenience caused! I have updated your Telerik points!
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