HTML and CSS Reference
Defining Values for Four-Sided Properties
Properties such as margin , padding , and border-width are used to
define values for all four sides of a block (whereas margin-right
defines the right margin alone). These properties, and those like
them, can take from one to four space-separated values that are
applied to the sides in the following manner:
■ If one value is listed (for example, 10px ), that value is applied to all
■ If two values are listed (for example, 10px 5% ), the first value is
applied to the top and bottom, while the second is applied to the
right and left sides.
■ If three values are listed (for example, 10px 5% 20px ), the first value
is applied to the top, the second to both the right and left sides,
and the last to the bottom.
■ If four values are listed (for example, 10px 5% 20px auto ), the values
are applied clockwise starting from the top (top, right, bottom, left).
At-rules are statements that begin with the character for at ( @ ), followed
by a rule type or identifier, and end with a semicolon. Unlike rule sets,
at-rules do not contain declarations directly but offer additional context
or commands for the processing of style sheet information. Here's an
/* include file additional.css */
/* target specific media with contained rules */