Preview shows hr lines differently

I noticed that two horizontal lines, with the same code, looked different in Sigil Preview. One line was thicker than the other.

But on my ereaders & in Calibre they were the same. Also the same in Sigil book view.

More of a curiosity, but I thought I would mention it.


html:

<h1>Title</h1>

<hr class="w50" />

<h2>Subtitle</h2>

<hr class="w50" />

css:

h1 { text-align:center; }

h2 { text-align:center; font-size:2em; }

hr.w50 { height:0.1em; border:white; background-color:black; width:50%; margin-left:25%; }


After testing I noticed it's the font-size element in h2 that makes the difference. If I set the size to 1em, the lines are the same. If I set it to something larger than 1, it gets thicker, but stays the same for any larger font-sizes.

(Sigil 0.9.10 on Linux)

Attached Thumbnails