I have a web app that has several tree views. When the page loads i see the unordered lists and after a small latency the styling of the tree is rendered into the DOM.

Is there a way to mask the webapp, and have a spinner in the middle of the screen, and when everything on the page is fully rendered the spinner goes away and the mask fades out? Kind of like a semi transparent mask that you would see on a lightbox pop-up dialog.