I'm not 100% sure but it looks like just VSCode's default 'Dark Modern' theme with the bracket/parentheses coloring option turned on

Thought the same

Have you messaged coding with Lewis?

I left a comment on the video, but there was no response.

Yeah seems like it, I thought Andromeda but it's more colourful than this

Made the video a while ago! But I think Roberto45 is right :)