Hi hep, the problem is that it makes a moi.css file based off of what MoI v3 used and doesn't have changes that were done for v4. The main thing that's different is that MoI v3 used the original webkit flexbox implementation which is now deprecated and v4 uses the standardized flexbox.

I've attached here a version of your customized moi.css that has the flexbox properties in it updated to what v4 is using, that should fix it.

- Michael