In the mx-element% method descriptions, “CSS” refers to the Cascading Style Sheets specification. A CSS length is string consisting of a decimal integer number followed by one of the units px (pixels), em (font height), ex (height of an “x”), in (inches), cm (centimeters), mm (millimeters), pc (picas), or pt (points). A CSS percentage is a string consisting of a decimal real number followed by %. When using -native methods, CSS lengths and percentages are given as strings. For use by non-native methods, the css-percentage and css-length structures have been defined.