I am trying to position images inside of a post such that the first image takes up the first column and 2 rows, the second image takes up the second column and the first row, and the third image takes up the second column and the second row. I am using CSS grid to try to accomplish this. The first problem is that the images go way beyond the images-container , as well as the other containers. The second problem is that the third image in the second row is pushed way below the first two images. In other words, the third image is not right below the first two images, but there is a space. Also, another problem is that the images-container stretches down beyond the bounds of the inner-post-container.
Concrete5 doesn't do anything to how images behave. It creates columns if you ask it to by using your own columns definitions. Or to be exact your theme's columns definition.
If anything you put in those columns is not behaving as you'd expect, it most likely is your theme's CSS that's at fault.