When using the latest editor we can choose under the Build Tab, "Layouts" and select a two column, or three column layout.
Shown in the screenshot above you can see "A" we can drag this into "B" but it will not go within it. It will try to place it Below the Two Columns.
Our goal would be to have two column layout within a two column layout. This will look like "C" which we are aware is possible with code but since your current editor removed HTML editing we're looking for this feature in your current editor. (So it remains responsive).
We look forward to hearing if this is possible in the near future.