It seems like a hacky solution as there should be an R Markdown fix, but here is what I landed on that worked to solve this issue. Note that Source Sans Pro and 16px are simply the defaults in quarto, so the html tag is matching those quarto defaults.

::: {#axm-real}
<p align="left" style="font-family: 'Source Sans Pro', sans-serif; font-size: 16px;">
text of axioms listed here
</p>
:::