So we will have to pick a theme. Of course we can keep the sphinx_rtd_theme but I guess this gives us the opportunity to choose maybe a better them for us.
I think we should limit our choice to https://sphinx-themes.org/ as they are supposed to be maintained.
We need to have a theme that is responsive, that render well python code and that render well the directives we use like menuitem, guilabel, warning, note etc. It is also good if we can make it looks like our website.
I will post a poll in few days after having collected thoughts or suggestions.
So I guess we could just define a theme for the latest version and we will have older versions rebuild with the default sphinx theme (instead of sphinx_rtd_theme). This will avoid to modify all packages of every supported series.
Accessibility is also an import measure. And looking at the performance, it is about the difference between 1.8 and 2.4 seconds. With high traffic websites that can be an issue, but for documentation I don’t think so.
But you also have to use the most recent version of the theme. I now see a big difference between Book Sample — Book (link from @udono) and Book Sample — Book (link for pagespeed). I have no idea which is the most recent one.
With the theme now active, I found that the main-content doesn’t keep the whole width but the minimum. This is not looking great. Changing the flex-grow from 0 to 1 of the .bd-main class will fix this. No idea if this can be added as custom css.