Is it built on some free script?
100% custom code good sir.

but why i can feel rollin.io when i visit your site? i assume you steal rollin's code and tweaked a little bit then boom new dice site.
I don't think they did. They would have to steal their frontend and make their own backend, but all that's similar is the big bet number in the middle and the names of the buttons and numbers. They could've simply just based their structure of their site on rollin, because rollin has a great UI.
EDIT - Where's the provably fair?
Click the Dice Icon directly below the Balance indicator.