This is the structure of a div (what we in WorldAnvil call containers).

In each div, there is the main content (blue box), where we will see all we have added inside the container.

Then we have the padding (green box), which is invisible space between our content and our borders.

The borders (yellow-box) are in between padding and margin, and they are the lines that (sometimes, when we set them) surround our containers.

Finally, we have the margin (orange-box). The margin is more invisible space, it surrounds our content and separates it from other content outside our div / container.