It would be ever so much easier if you used styles. My normal paragraph tag is
<p> and follows this style:
p {
margin-top:0.0em;
margin-bottom:0.0em;
text-indent:1.5em;
text-align:justify;
}
I don't want an indent in the first paragraph of a chapter or major section of a chapter, so I use the paragraph tag
<p class="first"> which not only eliminates the indent but adds a bit of space between the first line and whatever comes above it:
p.first {
margin-top:0.5em;
margin-bottom: 0.0em;
text-indent:0.0em;
text-align:justify;
}
You can copy or adapt my full style sheet from
https://notjohnkdp.blogspot.com/2013...yle-sheet.html
Add it to Sigil's "Styles" folder with the name epub.css (or whatever you like that ends in css) and put a pointer to it in the header.