CSS snippets are probably the best solution. If you know CSS, you can use the developer console (⌘ + option + i on Mac) to target CSS elements.
Obsidian uses Markdown, so there isn’t any built-in functionality for sub and superscripts, but you could possibly try MathJax, which is supported natively. It may not be exactly what you need, since it’s aimed at people creating math equations. Let me know if you have any questions 