looking for: code documentation note while hovering

Hello everyone,

I failed to bookmark a newish documentation platform where on the left side held the code, & when you hovered or clicked the [Next >] button, it would display a small note/documentation on the right side. Kinda like a screen cast, but advanced only on interaction.

Is anyone aware of this site please? By the blog posts (how I found it; google searching for something), it seemed only a few months old.

TIA

Thank you!