I'm trying to make an interface similar to that of whatsapp web which has a green header and a gray background where the chat box is contained on this gray background and the green header. The only way I can think of how this was done is by using divs. Assuming the green header and gray background are divs, and the box containing the conversations is another div, how do I make that div of the conversations overlap with the other divs?
AndwhatIwantisthis: