There are two types of numbers in CSS: integers ("whole" numbers) and reals fractional numbers). These number types serve primarily as the basis for other value types, but, in a few instances, raw numbers can be used as a value for a property.
In CSS2.1, a real number is defined as an integer that is optionally followed by a decimal and fractional numbers. Therefore, the following are all valid number values: 15.5, -270.00004, and 5. Both integers and reals may be either positive or negative, although properties can (and often do) restrict the range of numbers they will accept.