invisible del / "line-through"

I had some text that was supposed to be crossed out, it was formatted <strike>

-- editing the book in epub in Sigil, to export to azw3 using kindlegen.

<strike> seemed ok on screen and kindlegen had no problem, but epubcheck says "Error while parsing file 'element "strike" not allowed anywhere".

So I made a test page:
<h2><del>del</del><br/>
<strike>strike</strike><br/>
<s>s s s </s><br/>
<span style="text-decoration-line: line-through;"> text-decoration-line: line-through; </span><br/>
<span style="text-decoration: line-through;"> text-decoration: line-through; </span>
</h2>

epubcheck also whines about <s>

On Sigil preview, all work the same except "text-decoration-line" which has no effect.

Made AZW3 and loaded on a PW3 -- see screencap.

At first, I can see no lines at all. Peering closely, I see the line-through: it is just one pixel high. On a 300 dpi screen, this is imperceptible.

Are there any ways to get a thicker line-through?

Attached Thumbnails