The last item added is not visible once published

In my portfolio site, I’m trying to add a small subscription box at the bottom.

But whenever I add a div and give it a background (to give it a card look), even though it shows in the designer, the published one doesn’t show that div at all at the bottom. The page just ends scrolling on the previous section.

In the designer, the div also has a doted border on it. It becomes visible only if I add a child element into the div.

If I added a child element like a textbox in the div, the div becomes visible with its blue background, but now the textbox is no longer visible. It’s like the last child element is always invisible. In the published version, it just doesn’t exist.

Here is my site Read-Only: LINK
(how to share your site Read-Only link)