When defining custom counter styles, the range descriptor lets the author specify a range of counter values over which the style is applied. If a counter value is outside the specified range, then the fallback style will be used to construct the representation of that marker. Value of the range descriptor can be either auto or a comma separated list of lower and upper bounds specified as integers.
CSS Lists and Counters is a module of CSS that defines how lists are laid out, how the list marker can be styled and how authors can create new counters.
The ::marker CSS pseudo-element represents the marker box of a list item (e.g. the bullet point or item number).