These examples will work in most modern browsers. It is best to preview in both Safari/ Chrome and Firefox as there are significant differences in implementation. Note the position of the various divisions. Note also there is a wrapper with white background (which will bleed through in various browsers to demonstrate how they handle the flexible box model presently). Once this is properly implemented in most browsers, one can likely use a lot less floats (yippee).
Same boxes in same order, note placement with CSS, no floats involved.