Just wanted to point out a small bug I think I found. If it’s not a bug, my mistake.
When creating a grid in designer preview, using merged cells, the designer preview doesn’t display the positioning correctly, as it actually is when you view the site live. When you preview the site you can see that the grid is positioned correctly. This gave me a headache for quite a while because just going off the designer preview alone, I thought my grid was broken and not working properly. It wasn’t until I decided to just check site preview to see how it looked did I realize that it was perfect all along.
Here is the grid in designer preview, notice the giant white space underneath the squares of the left and right columns.
And here is how that exact same set up looks live, published and in site preview. So it’s working as it should, just not displaying properly whenever you’re building it.