Theme Conflict Fixer (or Upfront) Simple Calendar

I am enjoying this plugin: https://simplecalendar.io/ (simple calendar). It grabs all my google calendars and plonks them into one spot: http://www.fireflytheatre.com/calendar I don't like how it is displaying with lines not joining in the table and a scroll bar I don't want. The plugin devs were sadly not very helpful, except to say it is a *probably* a conflict with the theme.

I have tried targeting the offending elements, with very little luck. I have also spent some time with someone from Codeable, who is not totally able to help me.

How can I spot the conflict and resolve it?

I've added some code to style.css, which started to have an effect, but it's still not quite right.

Thanks, you guys rock the world.