In the Dashboard Widget regarding External Services, on the left side corner appears the control for resizing the widget as in the following figure.
In addition, the control reported below provides two small buttons (-) and (+) they can be used to zoom the web page of the External Service on Web page embedded.
This approacj is adopted in Synopic and other external services.
It has to be located in the <head> ...</head> of your main html page you are embedding.
Please remaind to place the file "zoomHandler.js" in the same path of your HTML file.