[Quoth]

And you can create that as a paragraph style in Word or LO Writer, then what DNSB has is automatically the CSS.

(12pt = 1em) If you want entire list indented to a 1.5 em regular paragraph first line indent.

Before Text: 36 pt /* wrap is 1.5 em in from first line. CSS margin-left */
After Text: 18pt /* CSS margin-right */
First Line : 18 pt /* i.e. negative compared to rest of paragraph. CSS text-indent */

Add a suitable amount for a nested list style.
Probably left justify. Adjust numbers to taste.

You can use different styles for first list item and last so that item spacing in the list is different from space at top of list and bottom of list.