HTML5 now has a native Dialog element, but it's not movable/draggable by default.
Thanks to this page, I was able to get this draggable demo going.
This is modal, and note that the above link is inaccessible when the dialog is up.
Also, my version restricts dragging to left-click. (In a web app I was coding, I was seeing weird behavior when middle/right-clicking it was allowed.)
Use CSS ::backdrop to style the backdrop overlay. Use `backdrop-filter:` to add the blur.