Length Units
A length value is formed by an optional + or -, followed by a number, followed by a two-letter abbreviation that indicates the unit. There are no spaces in a length value; e.g., 1.3 em is not a valid length value, but 1.3em is valid. A length of 0 does not require the two-letter unit identifier.
Both relative and absolute length units are supported in CSS1. Relative units give a length relative to another length property, and are preferred since they will better adjust to different media. The following relative units are available:
- em (ems, the height of the element's font)
- ex (x-height, the height of the letter "x")
- px (pixels, relative to the canvas resolution)
Absolute length units are highly dependent on the output medium, and so are less useful than relative units. The following absolute units are available:
- in (inches; 1in=2.54cm)
- cm (centimeters; 1cm=10mm)
- mm (millimeters)
- pt (points; 1pt=1/72in)
- pc (picas; 1pc=12pt)
Percentage Units
A percentage value is formed by an optional + or -, followed by a number, followed by %. There are no spaces in a percentage value.
Percentage values are relative to other values, as defined for each property. Most often the percentage value is relative to the element's font size.
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