HTML and CSS Reference
A percentage value is expressed as a <number> followed immediately by a percent sign ( % ).
There should never be any space between the number and the percent sign. A percentage
value will always be computed relative to something else. For example, declaring font-size:
120%; for an element sets its font size to 120% of the computed font-size of its parent ele-
ment. Some properties may restrict the values to be non-negative.