Ability to add body class with data-state

[marcysutton]

Some background image techniques are just easier when you can apply them to the body, like image border backgrounds. I can apply a bottom border with background-position: center bottom; background-size: contain; if it's on the body, otherwise I have to calculate the height of a slide element element and position it with pixels; either super error prone, or unnecessarily complex scripting when I just need to focus on slide content.

I wrote some custom CSS to add a default body background for all slides, but even with bgColor set on each slide it flashes the image when I change slides, which is distracting in a presentation. In reveal.js, you can use data-state to add a CSS higher up in the DOM tree than you have access to from a slide. It would be killer to have something similar so you can override CSS per slide in highly specific ways.