I don't know, I've been obsessed with detail of this sort for a while now. I wound up paying attention to things like this since I tried re-creating material design components in pure WebGL, It's stagnated now though: http://bollu.github.io/webgl-design/bin/paper-material.html
Combining Bootstrap with Material is like putting salt in coffee, and hiding with some sort of identity crisis. You've named expansion panels; accordions, which sure, they do follow a similar pattern, but which library are you basing the naming on?
As a front-end developer and designer, this makes me cringe.