Dropdown rendering in github but not RTD

[danamlewis]

#1551 moved some old information into a dropdown format...that is correct on github (dropdown works) but is not rendering in RTD (https://openaps.readthedocs.io/en/latest/docs/While%20You%20Wait%20For%20Gear/understanding-insulin-on-board-calculations.html).

It's matching the way it's done elsewhere, so there either is a change in how RTD is rendering it (unlikely) or there's something in this section that is breaking the formatting (more likely). I made several changes (66d9eb6, bc27dea, 29338f6, 536a2f2 ) to try to resolve but haven't found it yet, so leaving this issue as a reminder to hunt down why it's not correct in RTD. If you spot it, please PR the fix!