I have a requirement to show a modal with some text prior to creating a NEW record.   Ideally, a user would CLICK new to create a new opportunity, and would see a modal popup with text message.  She/he would then click a navigation button 'continue' to open the normal NEW record modal and create the new record.   No inputs are needed-  just a text message.  

I need this to work in Lightning and CLassic.  I wanted to do this with a FLOW/Process builder, but I see that you can't launch a screen flow from Process builder.   

How should I approach this so that it works in both Classic and Lightning?    

Thank you!