Length units define the size of element either as an absolute size or a size relative to its containing element. Any
property defined to accept a <length> value can accept any of the following units.
| em | The height of the element's font |
| ex | The height of the letter 'X' |
| px | Pixels |
| in | inches |
| cm | centimeters |
| mm | millimeters |
| pt | points, 1pt = 1/72inch |
| pc | picas, 1pc = 12pt |