Maybe we could add a CSS style that would address not only the size of sections, but also other issues, like responsive page size or images in dark mode. The question is whether to use it by default, or just by option. What speaks for default use is that, as Nasser noted, most users use the default settings and have no idea how to solve such problems. For users who want to use a custom style, we could provide an option that would ignore the default styles.

To my mind, this is a bug in the browser(s). Browsers should not render any <hN> tag as less than the body size. That's nonsensical.

But given that reality, and that it's unlikely to change, my suggestion for tex4ht is to avoid h5 and h6, since they are useless, and just use h4 for all those lower-level sectioning elements. Maybe with a class="subsubsection" or whatever so they can be distinguished if anyone cares to.

This seems cleaner to me than specifying explicit sizes for everything.

Reference and screen shot at

https://tex.stackexchange.com/questions/670328/inconsistent-font-sizes-used-for-subsubsection-paragraph-titles-in-tex4ht-how-t

I noticed in tex4ht that the size of the font used for the paragraph title is the same as that of the section title (i.e. too large) and the size of the font for the subsubsection is smaller than that used for the paragraph, which it should be larger or at least the same size.

This makes looking at titles confusing as font size gives indication of order.

The font size should decrease all the way from chapter to paragraph. Now it decreases but then starts to increase once it reaches paragraph.

in PDF, it is consistent, as the sizes decrease correctly from chapter to paragraph. Screen shots below

MWE

----------------------
\begin{document}
\title{my book title}
\author{me}
\date{\today}
\maketitle

\part{first part}
\chapter{first chapter}
\section{first section}
\subsection{first subsection}
\subsubsection{first subsubsection}
\paragraph{first paragraph}

\end{document}
-----------------------

Compiled using

make4ht -ulm default -a debug foo.tex 'mathjax,htm'

Gives

enter image description here

Compare to the pdf where the sizes decreases uniformly (but hard to see if font used for paragraph is smaller or same as subsubsection, but at least it is not larger like with the HTML)

enter image description here

Question is: How to make the size of the font used for paragraph title with tex4ht not be larger than subsubsection? Is there a way to control these settings?

TL 2022