The @font-feature-values CSS at-rule lets you use a common name in the font-variant-alternates property for features activated differently in OpenType. This can help simplify your CSS when using multiple fonts.
The @font-feature-values at-rule may be used either at the top level of your CSS or inside any CSS conditional-group at-rule.
Syntax
Feature value blocks
@swash- 
    
Specifies a feature name that will work with the
swash()functional notation offont-variant-alternates. A swash feature value definition allows only one value:ident1: 2is valid, butident2: 2 4isn't. @annotation- 
    
Specifies a feature name that will work with the
annotation()functional notation offont-variant-alternates. An annotation feature value definition allows only one value:ident1: 2is valid, butident2: 2 4isn't. @ornaments- 
    
Specifies a feature name that will work with the
ornaments()functional notation offont-variant-alternates. An ornaments feature value definition allows only one value:ident1: 2is valid, butident2: 2 4isn't. @stylistic- 
    
Specifies a feature name that will work with the
stylistic()functional notation offont-variant-alternates. A stylistic feature value definition allows only one value:ident1: 2is valid, butident2: 2 4isn't. @styleset- 
    
Specifies a feature name that will work with the
styleset()functional notation offont-variant-alternates. A styleset feature value definition allows an unlimited number of values:ident1: 2 4 12 1maps to the OpenType valuesss02,ss04,ss12, andss01. Note that values higher than99are valid, but don't map to any OpenType values and are ignored. @character-variant- 
    
Specifies a feature name that will work with the
character-variant()functional notation offont-variant-alternates. A character-variant feature value definition allows either one or two values:ident1: 3maps tocv03=1, andident2: 2 4maps tocv02=4, butident2: 2 4 5is invalid. 
Examples
Using @styleset in a @font-feature-values rule
/* At-rule for "nice-style" in Font One */
@font-feature-values Font One {
  @styleset {
    nice-style: 12;
  }
}
/* At-rule for "nice-style" in Font Two */
@font-feature-values Font Two {
  @styleset {
    nice-style: 4;
  }
}
…
/* Apply the at-rules with a single declaration */
.nice-look {
  font-variant-alternates: styleset(nice-style);
}
See also
- The 
font-variant-alternatesproperty that uses values that this at-rule defines.