There are number of values that may be assigned to a property, depending on its type.


Numbers may be integers or real numbers.

Some properties do not allow negative values.


Lengths refer to a measurement of distance.

They are expressed with a number followed by a unit identifier such as px, pt, em, etc...

If length is 0 a unit may be omitted.

Some properties allow negative length but it is suggested not using them for later formatting issues.

Two main types of length units are: relative and absolute.

Relative units are: em (the font size of the relevant font) and ex (the x-height of the relevant font).

Absolute units are: in (inches), cm (centimeters), mm (millimeters), pt (points = the points in CSS are equal to 1/72nd of 1 inch), pc (picas = one pica is equal to 12pt) and px (pixels = one pixel is equal to 0.75pt).


Percentages are represented by a number followed with a % sign.Values in percentages are always relative to another value, mostly to it's the inherited value of a given parent element's property.

URIs (URLs):

Uniform Resource Identifiers (URIs) are used to identify imported documents often attached as backgrounds or images.

The format of a URI value is url ('address') where address refers to an URI (i.e. Single or double quotes before and after the URI are optional.


Counter values come as one of two case-sensitive identifiers, 'increment' or 'reset' (counter-increment and counter-reset properties).

They are used as a way to number the sections and sub-sections within a document (very useful with lists).


A color value may be one of sixteen possible pre-defined keywords or a numerical RGB specification where RGB can be shown in a decimal, hexadecimal or short hexadecimal mode.

The color keywords are: aqua (#00ffff), <span style="color:black;>black (#000000), blue (#0000ff), fuchsia (#ff00ff), gray (#808080), green (#008000), lime (#00ff00), maroon (#800000), navy (#000080), olive (#808000), purple (#800080), red (#ff0000), silver (#c0c0c0), teal (#008080), white (#ffffff), and yellow (#ffff00). Their hexadecimal values are inside the apprentices.


String values can be written with single or double quotes.

For aesthetic or other reasons strings may be split with a newline but the newline has to be escaped with a backslash (\).


CSS color property values:


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