Symbols representing units in CSS

Css

The value of a length consists of an optional plus "+" or minus sign "-", followed by a number, and two letters indicating the unit. There is no space in the value of a length, for example, "1.3 em" is not a valid length value, but "1.3em" is valid. A zero-length two-letter unit declaration is not required.

Both the relative value and the absolute length are supported by CSS1. A relative value unit determines the length of a property relative to another length, because it is better adapted to different media, so it is preferred. The following are valid relative units:
EM (em, the height of the element's font)
Ex (x-height, height of the letter "X")
PX (pixel, relative to screen resolution)

Absolute length units depending on the output medium, so inferior to the relative units. The following are valid absolute units:
In (inches, 1 inches = 2.54 cm)
CM (cm, 1 cm = 10 mm)
MM (m)
PT (dot, 1 o ' =1/72 inches)
PC (PA, 1 PA = 12 points)

Percent Unit

A percentage value consists of an optional plus "+" or minus sign "-", followed by a number, and a percent semicolon "%". There is no space in a percentage value.
Percent values are used to define each property in relation to other values. The most commonly used percent value is the font size relative to the element.

Color units

A color value is a keyword or a number in RGB format.

Windows VGA (video image array) forms 16 keywords: aqua,black, blue,fuchsia,gray,green, lime,maroon,navy,olive, Purple,red,silver,teal, White,and Yellow.

RGB colors can have four different forms:
#rrggbb (e.g., #00cc00)
#rgb (e.g., #0c0)
RGB (X,X,X) x is an integer ranging from 0 to 255 (for example, RGB (0,204,0))
RGB (y%,y%,y%) y is an integer ranging from 0.0 to 100.0 (for example, RGB (0%,80%,0%))
The above example specifies the same color.

Unified Resource Management URL

The format of a URL value is: URL (foo), and foo is a URL (Uniform resource management, Internet address). The URL can optionally be in single quotes (') or double quotes ("), and can contain spaces before or after the URL.

Brackets, commas, spaces, single quotes, or double quotes in the URL must be avoided by backslashes. Incomplete URLs are understood as the source code of the stylesheet, not the HTML source code.