Ghostty supports iTerm themes, so you should be able to transfer your preferred look-and-feel directly. I just picked one I liked, so I'm not familiar with the process, but it can be done.
Here's the relevant docs page, which I hope explains why I mistakenly thought that transferring a theme directly from iTerm to Ghostty was possible. You could upload your theme to the website they're being sourced from, and wait a week. But that's clearly not the same thing.