When you place a container inside a form, the bottom margin doesn’t work as expected.
Basically the margin is applied by default on the dhx_form-group class selector but when the parent element (dhx_form-element class selector) is a container the bottom margin gets ghosted!
P.S.
In my case there is a dhx grid attached to the container.
Thank you for your report.
The problem was confirmed. We’ll try to fix it in one of the future updates.
For now as a workaround I can suggest you to add a padding under the container control: https://snippet.dhtmlx.com/a98o5ls4
I’ll inform you here when the fix becomes available.