How Do I Open VSCode's Extension Development Host Window?

I am currently trying to make my own color theme. I have made some in the past and have been able to test them through the extension development host window. The previous way to open it was F5, but now F5 is bound to debugging, so it no longer opens up that window. I have tried searching through settings and perhaps I am looking up the wrong thing, but it seems like the extension development window has virtually disappeared.