- All green boxes below are exactly the same size (style declares width and height).
- Boxes are defined as absolutely positioned and sized DIV elements.
- Box "two" contains an inner DIV with a 4px border one all sides and height of 100%.
- Box "three" contains an inner DIV with a 4px border on bottom and right sides and height of 100%.
The problem is that the inner DIV is too tall - by the sum of the thickness of the top and bottom borders.