Can preview's User Agent Stylesheet be disabled?

[KevinH]

Unfortunately, fonts and font foundries are idiosyncratic that way. One may draw a font and give it a font weight of 650 or 750 and call it "bold" while others call weights with 700 normal. The font engine and browser determine the mappings from numeric weights to descriptive terms and not everyone agrees. Qt has its own. Most times the definitions are similar and things work but sometimes not. It was worse in the old days when font metric info was stored in a second file.

If in doubt on Linux, fire up FontForge to get a full readout of what the font metadata and metrics actually say.

[st_albert]

Originally Posted by st_albert

Seems like one thing for me to try would be to build Sigil-2,1,0 on the older machine with Qt-5.15.10, and see how it behaves.

Not tonight though

Albert

Aww, what the heck. So I went and built Sigil-2.1.0 on the older machine per the instructions in Building_on Linux_older.md.
in the end, I have Sigil 2.1.0 with Qt 5.15.30 and as for the preview problem it behaves just like Sigil 1.9.30

So I guess this confirms it's nothing wrong with Sigil itself; but I'm not sure I have exactly the same fonts installed on both machines. BTW if a font substitution is made, is there any way to tell what font it decided to use? I always code a fall-bac font of, say, "serif" in any font specifications, and that has always worked before now ( and still does on other epub readers AFAIK).

again, using the same file on both machines, I get the following:

Albert

[st_albert]

SOLVED!
In my first post, I wrote:

Originally Posted by st_albert

I don't think this is a bug, but more likely ignorance on my part.

After absorbing all the advice presented above, especially Kevin's pointing me to font issues, it turns out my suspicion was correct. It was a PEBKAC problem.
After closely examining the inspector's "computed styles" column, I noticed that the rendered font was "aakar," which I think was a leftover from an over-zealous installation of foreign-language fonts by LibreOffice.
In contrast, on the machine that WAS displaying correctly, the rendered font was Times New Roman.
So on the problem machine, I deleted the "aakar" font. Now the rendered font became "Noto Serif" which behaves as expected with no modifications to the epub's CSS (e.g. changing font-weight: to 900 instead of "bold")

Many thanks to all the commentators for giving me the clues I needed!

Albert

[KevinH]

Glad to hear you got it working! And thanks for showing how to fix it!