[JSWolf]

Originally Posted by Quoth

I don't think so.
You can create CSS and then use regex to replace the stupid inline styles with the more sensible css Classes.

I suspect this is an old title perhaps made using some mad HTML3 software and a source MS Word with no use of paragraph styles.

Adding spaces won't work. The margins are wrong.

Edit
Replace margin:0.00% 0.00%; globally with nothing, in Sigil or Calibre as that makes no sense.

Replace style=" font-size:1.0rem" with nothing or all .0rem with .0em
Ebooks should never use rem
margins should never be 0.00%, or % at all. They are 0, or a number of em or at worst pt (1em = 12pt)
I'd only ever use % for an image width or an image height, with the other axis as auto. Nothing else should be auto.

azw3 and epub are a subset of HTML5.
Styles shouldn't exist, only CSS class names: Fivre line verse:
<p class="first-line">first line of verse</p>
<p class="verse-body">line of verse</p>
<p class="verse-body">line of verse</p>
<p class="verse-body">line of verse</p>
<p class="last-line">last line of verse</p>

Then the CSS sets top, left, right, bottom margins, text-align, font stuff

Edit
There are loads of ways to do it.

I'll disagree that margins should never be %. I have on instance where it's OK to be % and it's OK to change the size of the content. This is the CSS I use for section breaks.

hr {
  margin-top: 0.9em;
  margin-right: 40%;
  margin-bottom: 0.9em;
  margin-left: 40%;
  border-top: 2px solid;
}

As to the classes for first-line and last-line, get rid of them. Use a <blockquote> instead and just use the same class as the other lines.