Specifying values - Web Designing

It is important to use the proper syntax for specifying length and color values in style sheet rules.

Length Units
Table lists units of measurements that can be specified in style sheet values.

Table: Units of measurements for style sheet values

Units of measurements for style sheet values

Some values can be specified as percentages that are relative to the font size or bounding box of the element. The following example makes the line height 120% of the element's font size:

P {line-height: 120%}

Designers should keep in mind that the specific unit measurements listed above (pt, pc, in, mm, and cm) are not good choices for screen design because of the variation in size from monitor to monitor. It is preferable to specify sizes using relative measurements such as em and ex. Pixels (px) are acceptable as measurements for elements, but not necessarily for text.

Specifying Color
As in HTML tags, there are two methods for specifying color in style sheets: by name and by numerical values.

By name
You can specify color values by name as follows:

H1 {color: olive}

The CSS1 Specification specifically lists only 16 color names that can be used in style sheets; they are:

Other names from the complete list of color names may be supported by some browsers.

By RGB values
Within style sheets, RGB colors can be specified by any of the following methods:

The first method uses three two-digit hexadecimal RGB values. The second method uses a three-digit syntax, which is essentially converted to the six-digit form by replicating each digit (therefore, 00F is the same as 0000FF).

The last two methods use a functional notation specifying RGB values as a comma separated list of regular values (from 0 to 255) or percentage values (from 0 to 100%). Note that percentage values can use decimals, e.g., rgb(0%, 50.5%, 33.3%).

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