我怎样才能让一个div占据屏幕的全部宽度?

This might be simple, but I have a few nested divs that use media queries for sizing. I initially had box 3 as separate div below the container, but caused issues. So I included in the container and below the box 2 div. I would like for this div box 3 to take up the entire width of the screen.This might be simple, but I have a few nested d