Is there a way to support multiple zoom sliders on a single page?

Hi, great project thank you.

but one issue.. After closing element, error occurs (Firefox Quantum 59.0b4 Developer Edition):

TypeError: elem is undefined[Learn More]
classie.js:36:5
removeClass : .../js/classie.js:36:5
closeContent/< : .../js/main.js:189:4
onEndCallbackFn : .../js/main.js:27:56
onEndTransition : .../js/main.js:33:5
closeContent : .../js/main.js:188:3

i think problem was with elemement in function onEndTransition where this pointing to function(ev)... not to onEndTransition() (line 185):
onEndTransition(contentItem, function(ev) { classie.remove(this, 'content__item--reset');

try to change this to contentItem , like (line 185):
onEndTransition(contentItem, function(ev) { classie.remove(contentItem, 'content__item--reset');

works like a charm. Thanks for great work guys and keep it up!
Your fan m.