It looks like the process is more manual than I thought, sorry. There's something which imports themes from the iTerm2 color schemes website weekly, but from what I can find that isn't a feature which ships with Ghostty itself.

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.

https://ghostty.org/docs/features/theme