I’ve been playing around with it for a while, and I’ve found out that the issue is linked to the browser itself, in this case Chrome(android app). I’ve downloaded Mozilla(android), and it works smoothly.
By the way, I also noticed yesterday that the app didn’t work properly on some browsers e.g. Safari.
This is what it looks like on Chrome:
For some reason, the container(the outer border) is NOT shown on Safari.
Note: When I was creating the app, my intention wasn’t make it fully responsive, but what surprised me a lot was that it behaved so much differently on different browsers/devices.
Edit: solved solution