Hmmm… interesting challenge. Allow me to let out a few brain farts. I have never tried any of these ideas, I just like the mental challenge.
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Maybe using the draggable plugin? But I cannot imagine this being easy. @jdiaz has a great post which you could use for inspiration: Fluid transitions, are they possible on bubble?
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Could you lay 2 progress bars on top of each other for the visual and then lay a repeating group on top of all that with the page numbers?
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Maybe someone has already made this into a plugin? Otherwise, I would wonder: isn’t Discourse open source so couldn’t you just fork that code and build a plug-in?