To make a button using CSS:

<div style="text-align: center; background-color: #ffff66; margin: auto; width: 90px; border-radius: 15px; background: yellow; padding: 15px; border: solid 3px;"><a href="https://puestadelsolpta.org/##YourLinkHere##"><span style="font-size: 16pt; font-family: 'arial black', 'avant garde';">Tickets</span></a></div>

 

To generate links to add an event to Google/Outlook/Yahoo/etc calendar

https://www.labnol.org/calendar/