list-style-position: inside;

Yes! However, like I mentioned in my previous comment, corrections like this cancel out the number of bytes saved with the <ol>-based solution.

I mean, the solution in the original post is 152 characters long.

The <ol> based solution is 129 characters long. Shorter but uglier.

If we add your correction, we get neater output, which is nice, but it comes at the cost of 30 additional characters in the minified code thereby making the solution 159 characters long.

  li { list-style-position: inside }
  li:nth-child(3n), li:nth-child(5n) { list-style: none }
  li:nth-child(3n)::before { content: "Fizz" }
  li:nth-child(5n)::after { content: "Buzz" }