But... they aren't nested. HTML doesn't allow interleaved tags.
Here's a snippet of relevant page source:
<tr><td><h3><font color="red"><font face="arial">Improper Thread <br><width="25%" align="left"></font><font color="#0033FF"><font face="arial"> Try re-threading the machine; make sure the thread goes through all guides.</font></td></tr>
<tr><td><h3><font color="red"><font face="arial">Burrs <br><width="25%" align="left"></font><font color="0033FF"><font face="arial">There may be burrs in the needle's eye, on the thread guides, needle plate or the hook. Replace the needle and try buffing the thread guides and needle plate. Buffing may alter the timing, so it's a good idea to replace a damaged hook.</font></td></tr>
The <h3> tags are not matched by explicit </h3> tags. But they are closed; it isn't possible for the <h3> tag to extend beyond the boundaries of the <td></td> tag that contains it.
(Granted, there is no <table> containing these <tr> and <td> elements...)
> font-size: 1.17em;
Where is this applied? I'm looking in the page source and there are only six instances of `font-size`, none of which match this. There's one `<style>`, which doesn't have a font-size and doesn't style h3 tags. The string "1.17" does not appear in the source. The page inspector shows no styling applied to h3 elements.