The following repository hosts an example devcontainers spec. If you don't know what are devcontainers, take a look at Microsoft's documentation and Coder's. If you don't know Envbuilder, check out Coder's Github.
Envbuilder doesn't have 100% feature parity w/ Microsoft's Devcontainers. Refer to this list of available features.
For a very simple example, reference Coder's envbuilder-starter-container.
If you need to integrate new features into your devcontainer spec, reference this list.