I was kinda surprised that this method wasn't included in the article. While I use flexbox for centering most of the time, I still find myself resorting to the absolute positioning way sometimes.
Spending quite some time in both Malaysia and Thailand I can say that the support for cross country payments is still not great. I’m rarely able to use my Malaysian banking app (Maybank) to pay in Thailand. Most of the times when I tried the QR code is not recognized. Which means I still need to carry cash with me all the time.
Those shadows are smooth indeed, very cool project!
Small suggestion is to make the box to which the shadow is applied resizable. How we want the shadow to look often depends on the size of the element to which it is applied.
Could be as simple as adding this CSS to the box: resize: both; overflow: auto;