Atomic Tuesday

Hello, I am looking for a how-to for creating drag bars (whether vertical or horizontal) similar to the ones that are shown on W3Schools' Try It Yourself editor. In those examples, the drag bar separates the code from the displayed working example. My suggestion is to add a how-to for creating drag bars. W3Schools is an awesome site with an amazing amount of information for anyone to learn. This has helped me significantly in our journey of learning web development. Thank you,