docs on slide backgrounds
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+## Slide Backgrounds
+
+Slides are contained within a limited portion of the screen by default to allow them to fit any display and scale uniformly. You can apply full page backgrounds outside of the slide area by adding a data-background attribute to your slide header element. Four different types of backgrounds are supported: color, image, video and iframe. Below are a few examples.
+
+ ## CSS color background {data-background=#ff0000}
+
+ ## Full size image background {data-background="background.jpeg"}
+
+ ## Video background {data-background-video="background.mp4"}
+
+ ## Embed a web page as a background {data-background-iframe="https://example.com"}
+
+Backgrounds transition using a fade animation by default. This can be changed to a linear sliding transition by specifying the `background-transition: slide`. Alternatively you can set data-background-transition on any slide with a background to override that specific transition.
+
## Reveal.js Options
Reveal.js has many additional options to conigure it's behavior. You can specify any of these options using `reveal_options`, for example: