This members-only tutorial provides the steps to apply UIKit for Oxygen's Modal components so they work better especially when there is overflow compared to the earlier shared fix.
Live Demo (scroll down until you see the Open Modal button)
Load UIKit in your WordPress site by following Step 1 of this tutorial.
Let's add markup (data attributes, classes) and insert the close button as needed by UIKit using some custom jQuery. The code is set to handle multiple modals and need not be edited after it has been added.