In the initial design of a box model layout, create a HTML box and insert 2 items, one to float left and one to float right. After the fact, how do you go back and create an additional item, say like a spacer, that extends across the bottom of the box below the other 2 items?
If you click inside the container that holds all of the elements so that you have a flashing text cursor, you can use the arrow keys to move that cursor until it is between or after the elements where you want your spacer to appear. Then just use Insert > HTML Item or Graphic item, and resize the resulting inserted element afterward. Another thing to try (if you’re after some spacing between elements) is to use margin or padding to do the same thing without adding another element.