Whenever I like a syntax highlighter theme on a website, I search on Github a few of the hex codes. Like this: https://github.com/search?q=65ddd9+ff767b+ffc312&type=Code

In this case, there's only 1 result… the author's public repo. So I guess the search worked! But the theme seems to be a personalised one the author created themselves.

But the primary colors remind of Solarized Dark, if that helps: https://www.google.com/search?q=solarized+dark&tbm=isch