Thanks Frank! I was going through the same thing today.
You can take this method one step further to get rid of the underline too:
<span style="color: #ffffff; display: inline-block; text-decoration: none;">Add to Calendar</span>
By adding the display: inline-block tag, you can then apply any text-decoration styles directly on the span and have them override the parent <a> tag.
Was truly looking all over the community for this solution. Thank you so much!