Animating via CSS transition and the manipulation of custom CSS variables (which will, of course, end up as plugin parameters) from Javascript. Bootstrap class name congestion can go ahead and f$&k off now.
@brid.gy In this case I was just recreating the collapse feature of Bootstrap, nothing exciting. The cool part is having Hugo parameter values become Sass variables which become CSS variables and then using Javascript to manipulate some of the CSS variable values set directly on the collapsible input field.