At-rule @counter-style

Lets you extend predefined list styles and define your own counter styles that are not part of the predefined set of styles.

Examples

@counter-style thumbs {
  system: cyclic;
  symbols: "\1F44D";
  suffix: " ";
}

ul {
  list-style: thumbs;
}
@counter-style circled-alpha {
  system: fixed;
  symbols: Ⓐ Ⓑ Ⓒ Ⓓ Ⓔ Ⓕ Ⓖ Ⓗ Ⓘ Ⓙ Ⓚ Ⓛ Ⓜ Ⓝ Ⓞ Ⓟ Ⓠ Ⓡ Ⓢ Ⓣ Ⓤ Ⓥ Ⓦ Ⓧ Ⓨ Ⓩ;
  suffix: " ";
}

.items {
  list-style: circled-alpha;
}

Source MDN