Since the documentation was updated to use intersphinx, instead of submoduling other repos, I believe this issue can be closed.

VTR does use the readthedocs theme, indeed. However, that's legit, because they build their own docs (https://docs.verilogtorouting.org/) and they decide which theme/style they want to use. Should they want to change the theme, it can be done, but it should be tracked in https://github.com/verilog-to-routing/vtr-verilog-to-routing.

I think working with the upstream project to use the nicer theme would be good.

Closing due to verilog-to-routing/vtr-verilog-to-routing#2006.