Assuming it uses PHP, there are only so many ways to write a site like this..
Regardless, the CSS is a part of any source... So yes, they do have VERY similar source codes.
It's fine, I'm just wanting to see something unique.
I've used twitter bootstrap for my frontend, as do many bitcoin sites, due to its ease of use and quick development time. I hadn't actually seen coinroll.it untill one month ago, after I had been developing this for quite some time. The actual bootstrap template I was working with reference to was this
http://getbootstrap.com/2.3.2/examples/marketing-narrow.html, so you can see how both coinroll.it and I use the same layout.
This however doesn't mean that our source codes are even remotely similar. Please read through the HTML and JavaScript, I'll be publishing it on GitHub soon, also our backend is written in Python, our uniqueness doesn't come from our frontend however. We have implemented Bitcoin message signing which makes our game both provably fair and off-blockchain, something no other service currently offers.
Site will be going down for maintenance, while I fix a couple of bugs which weren't present in staging.