i guess conclusion is not a bug? closing.

I think this is a bug, so to be safe, I am reporting here as well.

Cross posted at

https://tex.stackexchange.com/questions/474282/tex4ht-css-code-works-using-standard-book-class-but-has-no-effect-using-koma-sc

I am using a \Css configuration which centers a caption under a figure thanks to https://tex.stackexchange.com/questions/472625/how-to-make-caption-be-centered-under-table-when-using-tex4ht

Now I find this does not work if I change document class to koma-script !

Here is a MWE

----------------
%\documentclass[11pt]{scrbook}
\documentclass[11pt]{book}

\usepackage{graphicx}
\usepackage{float}

\begin{document}

\begin{figure}[H]
\centering
\includegraphics[width=0.5\textwidth]{example-image-b}
\caption{test image}
\end{figure}

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

Now compiled using make4ht -c my.cfg where my.cfg is

\Preamble{xhtml}
\Css{div.caption{text-align:center;}}
\Css{div.figure img {text-align:center;display:block;margin-left:auto; margin-right: auto;}}
\begin{document}
\EndPreamble

Gives the expected output with the caption right under the image.

Now changed the document to

\documentclass[11pt]{scrbook}

And making no other changes and compiling again using same command, gives the caption no longer centered under the image. Meaning the CSS code had no effect.

Why would changing the document class makes the CSS configuration have no effect?

TL 2018