Can't get this working

[MrChriZ]

Am I missing something obvious:
I can't get this to work.
I've created a quick twiddle that demonstrates my issue here:
https://ember-twiddle.com/dc010f76afe81a62119709f0a3fa8bb6?openFiles=templates.application.hbs%2C

[sheriffderek]

For some reason, For some reason, you have to set height on the .flickity-viewport (which should be calculated) - and it doesn't seem as though it's an imagesLoaded issue - because resizing the browser doesn't do the trick. It's not you.

https://ember-twiddle.com/ea3e589653c75d6d33a5488c5db31081?openFiles=styles.app.css%2C