How to render text boxes on Send to Kindle EPUB KFX

If you send an EPUB with fieldset tags that put boxes around text through Send to Kindle, those boxes won't render.
Most EPUB readers add default CSS to fieldset tags.
www.w3schools....
But apparently Send to Kindle KFX is not one of them.
So you need to add this CSS manually.
Send to Kindle ignores fieldset default css that adds boxes and margins around text, so I convert the fieldset to span and add the missing css manually. system is just a name, I could have called it `anything`
www.mobileread...
Calibre convert to EPUB:
Look & Feel: Styling: Extra CSS
Code:
.system {
display: block;
margin-left: 2px;
margin-right: 2px;
padding-top: 0.35em;
padding-bottom: 0.625em;
padding-left: 0.75em;
padding-right: 0.75em;
border: 2px groove;
}
img {
height: auto !important;
width: auto !important;
max-width: 100%;
display: block;
}
Look & Feel: Transform HTML
If the tag is fieldset
change tag name span
add classes system
Page Setup: Output Profile: Tablet (at the bottom)
Epub Output: EPUB VERSION 3!!
then upload via Send to Kindle website.

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I am using the official Amazon Kindle Previewer app to quickly check the epub results.