HTML and CSS Reference

In-Depth Information

meaning as the intensity of the primary colors increases, the color becomes lighter

and lighter (the lightness is added to) until eventually it becomes white. To define

color in a web browser, each primary color is stored in a byte, or 8 bits (8 ones and/or

zeros). Each color component (red, green, and blue) then has the possible values in

the range of 00000000 to 11111111, which is the range 0-255 in decimal. 0 is com-

plete lack of the color, while 255 is the fullest possible intensity of the color. Decimal

is a base-10 counting system, meaning ten digits (including 0) are used before count-

ing moves position. Binary is a base-2 system, meaning only two digits are present

(0 or 1). Base-16, hexadecimal, has 16 digits that can be used to compress a binary

number, such as 1111, into one digit: F. The following table shows the first 16 digits

of each numbering system:

The value 255 in decimal can be represented as 11111111 in binary or FF in hexa-

decimal. Obviously, at two digits long, hexadecimal wins as the most compact rep-

resentation of the number 255. Pure white, which is the combined full intensity of

red, green, and blue, can be represented as red = 255, green = 255, and blue = 255,

or in hexadecimal as red = FF, green = FF, and blue = FF. Condensed all together we

get FFFFFF. Add a hash sign to the beginning, and this is the hexadecimal notation

used for colors on the Web. The range of colors available in this system is 256 × 256

× 256 (or 2563), which equals 16,777,216 possible colors. (256 is used here instead

of 255, because the calculation needs to factor in zero in each color component.)

that integrates into Firefox and provides several features such as an in-browser color

picker, web page color scheme analyzer, and even a tool for creating CSS gradients!

Hexadecimal notation can also represent color using three digits when a digit is re-

peated in each of the color components. So, magenta could also be represented as

#f0f
. White, which is
#ffffff
in hexadecimal, can be optionally shortened to
#fff
.

#99aaff
(a light blue) could be shortened to
#9af
, and so forth.

It is also possible to use a preset color keyword such as
white
,
black
,
aquamar-

ine
, and so on. While modern web browsers support dozens of keywords for choos-

ing colors, for the sake of consistency stick with precisely defining your colors (through

hexadecimal notation or otherwise) to ensure they are the same as what appear in your

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