Serving an Iframe in Google Colab Notebook: localhost refused to connect

I am trying to serve some HTML from a Google Colab notebook using the following:

from IPython.display import IFrame

IFrame(src='./output/index.html', width=700, height=600)

However, this throws localhost refused to connect:

Does anyone know how I can serve the html in index.html (which must load javascript) inside the Colab notebook? Any pointers would be hugely appreciated!