How do I create a custom theorem matching the existing theme?

[jj-marr]

I want to create an environment called "goal" and have it be formatted the same way as a theorem. I'm unsure of how to do this in an efficient way.

[Jinwen-XU]

There is currently, unfortunately, no user-interface commands for directly achieving this, but it would not be very hard to simply replicate the internal code. I shall see if I could come up with some better method this weekend or next week.

Meanwhile, if you just want something with the same style as theorem, perhaps you could try theorem-with-name. With \begin{theorem-with-name*}{Goal} or \begin{theorem-with-name}{Goal}, you should be able to get the desired visual effect, though you probably wouldn't be able to reference it.