::marker shapes the sign of the list

In a few sentences

In brief

The number or point can be changed without removing the list structure.

Useful to know

::marker selects the marker box for items with display: list-item. This includes the numbers and points of the usual lists. A limited set of CSS properties is supported. [1]

Example: li::marker { color: darkgreen; font-weight: bold; }. The line text remains separate and the list retains its HTML structure. Do not expect any property for boxes, such as arbitrary sizes and frames, to work on the marker. When the task is simply a different color of numbering, this approach is more direct than manually typing all the numbers.

Sources

For further detail and to check the information:

[1] MDN — ::marker ↗