In all other cases, margins of various elements do not overlap, and are always within its containing block. I have colored the margins, border, padding and content area of the paragraph gray, red, yellow and white respectively in the diagram above, but there's no way to actually have them appear like that in a document.
Margins are always transparent.
The padding and content area both have the same color, which is set with the background-color property. The border is a thick solid yellow line. Both the content area and the padding have a green background. So, enough with the refresher course. I hope it jogged your memory, let's go on to a demonstration of floats.