Allows definition of a custom counter style. The general form of an @counter-style rule is:
@counter-style <counter-style-name> { <declaration-list> }Counter style names are case-sensitive, However, the names of counter styles that are predefined in CSS Counter Styles Level 3 are matched case insensitively. A counter style name cannot match “none”, and “decimal” and “disc” cannot be defined as counter style names.
The following descriptors are allowed in the declaration list:
system : Specifies which algorithm to use to construct the counter’s representation.
negative : Defines how to alter the representation when the value is negative.
prefix : Specifies a symbol that is prepended to the marker representation.
suffix : Specifies a suffix that is appended to the marker representation.
range : Defines the ranges over which the counter style is defined.
pad : Specifies a symbol with which to pad counter representations that are not a minimum number of grapheme clusters.
fallback : Fallback counter style to be used when the current counter style cannot create a representation.
symbols : Symbols to be used by the marker-construction algorithm.
additive-symbols : Symbols to be used by an additive marker-construction algorithm.
speak-as : Describes how to synthesize the spoken form of a counter.[12]