[Shori]

I edited the stylesheet all by myself. Here it is:
----------------------------------------------------

Spoiler:

*{
text-align: justify;
}


a{
text-decoration:none !important;
color: Black;
}


body{
orphans: 2;
widows: 2;
font-size: 0.85em;
}

p {
font-size: 0.85em;
text-indent: 1.5em;
margin-top: 0;
margin-bottom: 0;
orphans: 2;
widows: 2;
text-align: justify;
line-height: 1.4em;
display: block;
}


/* Linea*/
hr {
align: center;
color: black;
weight: bold;
noshade;
padding-bottom: 0;
padding-top: 0;
margin-left: 20%;
margin-right: 20%;
margin-top: 0;
}


/* Intestazioni*/

h1, h2, h3, h4, h5 {
margin-top: 0;
margin-bottom: 0;
}

h5.spec3 {
font-variant: small-caps;
line-height: 1.3em;
text-align: center;
margin-top: 3em;
margin-bottom: 2em;
font-weight: normal;
page-break-after: avoid;

}

h3.spec1 {
page-break-after: avoid;
line-height: 1em;
text-align: center;
margin-top:1.5em;
margin-bottom: 1em;
font-weight: normal;
margin-left:2%;
margin-right:2%;
}

/* Def Titolo Indice*/
h2.ind {
page-break-after: avoid;
line-height: 1.3em;
text-align: center;
margin-top: 1.5em;
margin-bottom: 1em;
font-weight: normal;
font-variant:small-caps;
}

/* Def titoli capitolo*/
h2.tcap {
page-break-after: avoid;
line-height: 1em;
text-align: center;
font-weight: normal;
font-variant:small-caps;
font-size:1.7em;
margin-top: 0.5em;
margin-bottom: 1em;
}

h4.cap {
line-height: 1.3em;
text-align: center;
margin-top: 1.5em;
margin-bottom: 0.3em;
font-weight: normal;
page-break-after: avoid;
}

/* Frontespizio*/

h3.fro {
page-break-after: avoid;
line-height: 1.3em;
text-align: center;
font-weight: normal;
margin-top: 5em;
margin-bottom: 1.5em;
hyphens:none;
-webkit-hyphens: none;
}
h2.fro1 {
page-break-after: avoid;
line-height: 1em;
text-align: center;
font-weight: normal;
font-size:1.7em;
text-transform:lowercase;
letter-spacing: 0.2em;
font-variant:small-caps;
hyphens:none;
-webkit-hyphens: none;
}

div.fro2
{
margin-top:35%;
height:15%;
width:100%;
display:inline-block;
text-align:center;
}


/* Riga vuota*/
.rigavuota {
display: block;
border: currentcolor none 0;
margin-top: 1em;
margin-bottom: 1em;
}

/*Inizio capitolo in maiuscolo*/
.corpo1 {
text-transform: uppercase;
font-size: 1.1em;
}


/*maiuscoletto nel testo*/
.corpo3 {
font-variant: small-caps;
text-indent: 1.5em;
display: block;
}

/* corpo testo*/
p.ind2 {
line-height: 1.5em;
display: block;
text-indent: 1.5em;
margin-left:0;
margin-right: 0;
}

p.ded {
line-height: 1.3em;
display: block;
text-align: center;
font-variant: uppercase;
margin-top: 2em;
margin-bottom: 1em;
font-weight: normal;
font-size: 0.78em;
page-break-after: avoid;
}

p.ded1 {
line-height: 1.3em;
display: block;
text-align: center;
font-variant: uppercase;
font-weight: normal;
font-size: 0.78em;
page-break-after: avoid;
}


/* interruzione di pagina */
.pagebreak {
borde-bottom: 0;
border-top: 0;
dispay: block;
padding-bottom: 0;
padding-top: 0;
text-indent: 1.5em;
margin: 0;
}


/* Copyright */

p.cpr1 {
line-height: 1.3em;
text-indent: 0;
margin-top: 0.5em;
margin-bottom: 0;
}

p.cpr2 {
line-height: 1.3em;
text-indent: 0;
margin-bottom: 1em;
}

p.cpr3 {
line-height: 1.3em;
text-indent: 0;
font-style: italic;
margin-bottom: 1em;
}

p.cpr4 {
line-height: 1.3em;
text-indent: 0;
font-style: italic;
margin-bottom: 2em;
}

p.cpr5 {
line-height: 1.3em;
text-indent: 0;
margin-top: 2em;
margin-bottom: 0;
}

---------------------------------------------------------

I am not new to html, but I am to ebook. And you are right about the javascript file. I added it yesterday, so as all those "KoboSpan" I confess I don't know what they are for.
But deleting the kobo.js and all the Kobospans, I get just the same result. So I suppose the answer is not there.

I don't understand what's the trick.
You have no idea how many tests I have made so far.