I am not sure if there is an OOTB to hide some DIV while printing, but this can be achieved in this following manner.
On a click event of a button configure the below steps in order.
1) Hide the LIVE UI option by configuring Run Script. Define your own js method which can hide a DIV based on some attribute eg. data-test-id=UIInspectorButton. You can check the below fiddle for better understanding
2)Use the Print Action as you are using currently.
3) Refresh section.
In this way, you should be able to hide the LIVE UI while printing & it will not appear in the PDF.
I think some of us might misunderstood the requirement. The requirement is to hide the liveUI only in the pdf generated and not otherwise.
So, as suggested in step 1) add an action runscript. Define your own js method and use that function in userwork form and use the below code.
var divID = document.getElementById("js-toggle-runtime-editor");
Adding the css may not help since it will hide the LIVE UI completely which I think is not the usecase. Please correct, if I misunderstood something.
Please let me know if you need further clarification on this.