Lengths and Percentages

There are many property-specific units for values used in CSS, but there are some general units that are used in a number of properties and it is worth familiarising yourself with these before continuing.

em (such as font-size: 2em) is the unit for the calculated size of a font. So "2em", for example, is two times the current font size.

px (such as font-size: 12px) is the unit for pixels.

pt (such as font-size: 12pt) is the unit for points.

% (such as font-size: 80%) is the unit for... wait for it... percentages.

Other units include pc (picas), cm (centimetres), mm (millimetres) and in (inches).

When a value is zero, you do not need to state a unit. For example, if you wanted to specify no border, it would be border: 0.