Ok. Looks like you are using the embed as an iframe option. If you want full control over the styling, you will need to set the form to us raw html. Then you will have complete control over the style.
Seeming this is live, I would clone it and add the clone to a test page and mess around. You probably knew that already 🤣
On this page is a reference to the raw html option (it is far down on the page)