[phossler]

Maybe create your own CSS in

.....\AppData\Roaming\calibre\resources\templates\ inline_toc_styles.css

to use in the In Line toc.xhtml

Spoiler:

li > ul {margin-bottom: 1em;
}

ul.level1 {
  padding-left: 0;
  font-weight: normal;
  font-size: 100%;
  margin-top: 1em;
  margin-left: 0;
  text-decoration: none;
}

ul.level2 {
  font-size: 100%;
}

ul.level3 {
  font-style: normal;
}

li {
  margin-top: 1em;
   list-style-type: none;
}

a { 
  text-decoration: none;
 color: black;
}

a:hover {
 border-top-style: solid;
  border-bottom-style: solid;
  padding-bottom: 2px;
 padding-top: 1px;
 border-top-width: 2px;
 border-bottom-width: 2px;
 color: white;
 background-color: black;
}
h2 {
  page-break-before: always;
  page-break-after: avoid;
  text-indent: 0;
  text-align: center;
  margin-top: 0;
  margin-bottom: 1em;
  font-size: 2.5em;
  font-weight: bold;
  font-style: normal;
  font-family: sans-serif;
}