This looks really cool.

I wanted to mention that iCYOA can do this, but isn't not be suited for it. If you want to give it a go, just use a CYOA as the background and make a theme which focuses on opacity hover and select effects. I have added direct CSS editing now so it should be a little easier, and remember you can share your theme with others. There is absolute positioning on all components, which when selected allows you to change the position relative to its parent. Just be careful with things like height and width as absolute components arnt considered "in-flow" which means the parent will not resize to fit it (and check your overflow value). Also, if you're moving things around "in space", make sure you keep an eye on the hierarchy, which is in the navigation. Just because you change somethings position so it is in another box, it doesn't mean its in that box in isn't in the hierarchy, and that's what matters for things like limits and default variables.

I was thinking about adding direct positioning and resizing (such as you may find on an image manipulation program) when its position is set to absolute. If overlaying interactivity is popular, I think it would be a good edition, what do people think?

Sorry for commenting on your post like this to promote my own site. Its really scummy. Again, your site is really cool, especially how easy it is to create boxes with a simple click and drag. Just drop me a message if you wanna chat.