Superscript size mismatch for main author, extra author and affiliation text

[rikudoukarthik]

I believe this issue is present in all three templates, posterdown_betterland & posterdown_betterport & posterdown_html (v1.0).

There are size differences in the superscript numeric value given to each affiliation, between that of the main author(s), extra author(s) and affiliation text. After some digging in the output HTML file, I realised that the CSS styles produced specify .affiliation sup {font-size: npx;} and .author sup {font-size: npx;} by default (I don't remember what n exactly was), but don't do so for .author_extra.

This would still be fine I guess when using the template default text sizes for author and affiliation text, but in my case I used a larger font size for both and this led to an unappealing size mismatch. This looks worse because the main author text size is bound to be larger than that of the extra author, but the superscript size remains much smaller (while in author_extra since there is no value specified for sup it calibrates with the specified text size).

I was able to adjust the superscript size of main author using a CSS code chunk after the YAML and setup chunks, but for some reason the same did not work for the affiliation text.

```{css}
# for main author affiliation superscript
.affiliation sup {
font-size: 40px;
}
.author sup {
font-size: 40px;
}```

In my opinion, it's best to just remove all default superscript size settings. If the user wants to adjust it, they can simply specify it in CSS code chunks.