I’ve styled a Popup and a video in it so that once Play button(a link) is hit on, it opens the popup and instantly plays the video (this is normal). But now I need the page to automatically do the work once it loads. i.e Automatically display the Popup and plays the video.

I had a button that change page theme to dark-mode. when you click on, it works but when refershing the page, changes will be not save. pls help me to fix that????????