Stylus is a free browser extension that re-interprets CSS on the fly. (I don't know how computer savvy you are, so ignore anything you already know). CSS is the styling language that determines how a page looks in your browser: fonts, colors, position of elements and more. With Stylus, you can put in a rule that says, "when I visit app.Roll20.net, please change these specific rules about the appearance of these specific elements." People use Stylus to give their favorite sites a "Night Mode", or to enlarge or hide particular elements they like or don't like. There are thousands of themes and rules out there to download. Basically, you install the extension, create a rule, put in the code and tell it on what sites you want it to run. I don't know of any that change the deck position, but you might be able to solicit suggestions or help from the community to create the code that moves it.