Have you tried html's ordered lists? There are also various sites on the web that explain how to make them prettier than they are without any CSS styling.
https://www.w3schools.com/html/html_lists_ordered.asp
Also, rather than use a style= on each tag it's better to use a stylesheet.
https://www.w3schools.com/css/css_howto.asp
With sigil you put it in the Styles folder, then right click on the html files and select your stylesheet to link it and sigil ands the link rel= for you with the proper path.