Overall it looks fine. Some quibbles on the wording and the test.
Removes vertical and horizontal white space margins.
the 4.  (top, left, bottom).
I'm not sure if there some wording that can clear that up in the first line.
- There should be tests of align(n) with negative values.
- The for for for for structure doesn't follow the style guide.
> Please review the code  for  String::align and String::indent at the link below.