<hr> doesn’t show any line, why?

Not sure this is what you need but I have used it before:
https://www.pageresource.com/html/hr2.htm

If you’re talking about the blog at: https://lnx.sinapsi.org/wordpress/

Then, in your style.css file, you have this:

.skip, hr{
	position: absolute;
	left: -9999px;
}

That’s pushing your hr’s off the page.

Thanks Otto42
But now that I understand the reason of the problem, which is the solution? Remove those lines? Or what?
many thanks

Change the code to this:

.skip {
	position: absolute;
	left: -9999px;
}

That will leave the .skip class intact (I assuming that’s applied to elements that you want hidden), but will let the <hr> appear as it does by default (unless there’s another line in your CSS file that does something else to the <hr> tag; I haven’t looked at the stylesheet).

If you want to style the <hr> tag, you can put it in the CSS file on its own:

hr {
    [colors, width or whatever]
}

If you don’t know CSS and want to learn, I found the Westciv site very helpful when I was learning CSS. You don’t have to purchase the guide, they have all the basics online.

If you’re delving into modifying your own WordPress site, it is well worth your while to learn CSS, since that controls most of the look of your site.

To: StrangeAttractor
thanks for you suggestions, I’ll apply.
I didn’t do that CSS as I hardly know how it works. I suppose those lines are supposed to work with that fluid theme.