Floating and clearing

This isn't a Tetris board. Well, maybe it is. But it's also a demo of how floats and clears behave.

Notes

Use text-shadow to help the numbers stand out against their backgrounds.
Try making the line-height of the boxes the same as their height. You know how line-heights affect text in paragraphs, but its useful to think of them in relationship to other elements.
The order of the boxes in important. If two boxes float right, the first one will be further right.