<span> is an inline element, while <div> is a block element. @PaulOB explained the difference to you yesterday. Does and should [display values] be put on every style tag? - #5 by PaulOB
See also this part of the article: https://developer.mozilla.org/en-US/docs/Web/HTML/Block-level_elements#Block-level_vs._inline
As far as the original question goes:
Should I be using span style, or div style
the answer (as you’re well aware) is “neither”. Using inline styles is an outdated practice. You should b using the appropriate HTML element with external CSS styling.