Embed Element Changes Other Styles

I created a website for a charity and just used the embed element to add a donation form from iATS, a payment processor. It’s a embed. The problem is that the form I created on their site is leaking its style onto the rest of my page, too. Most notably, it’s changing links in the header and footer, both of which are symbols.

Any advice would be much appreciated.

Here is the live site where you can see the problem (compare header on this page to other pages):

Here is my site’s read only link:

Thank you in advance