Eclipse Theia is consumable in the form of npm packages (namespace @theia).
Here is an example application that we build from Theia called Blueprint (repo: eclipse-theia/theia-blueprint). For more information about Blueprint, please see here. Below are direct links to the latest version. Note that Blueprint is considered Alpha software at this time.
You may need to right-click on the wanted package and use "save link as" or such.