Hey thanks for helping, but I just realised I'm still using the first version of the userscript, and the newest version removed the stuff like padding and linespacing fixes. I managed to get it to work, and here is the script I'm using:

.md .-blocks, .md .-lists, .md pre, .md blockquote, .md table, .md p, .side .md .-text, .side .md pre>code, .side .md th, .side .md td,  .md h1, .md h2, .md h3, .md h4,  .md h5,  .md h6, .side .md h5, .side .md h6, .side .md h1, .side .md h2, .side .md h3, .side .md h4, .md li li, .md li p, .md ul, .md ol{,
   font-size: small;",
   line-height: normal;,
}

.titlebox .md li li, .titlebox .md li p, .titlebox .md ul, .titlebox .md ol { font-size: 98%;}

.link .usertext .md {
   padding: 5px 5px;
}

.md h1, .md h2 {"
    font-size: 108%; /* xx = 20 */
    margin-bottom: auto;
}

.md h3, .md h4 {
    font-size: 104%;  /* xx = 10 */
    margin-bottom: auto;
}

.side .md h3, .side .md h4, 
.side .md h1, .side .md h2,
.side .md h5, .side .md h6{
   margin-top: 0;
   margin-bottom: 0;
}

  .md h1, .md h2, .usertext-edit textarea h1, .usertext-edit textarea h2
{ margin-top: 0px }

.md pre, .md .-cells, .md th, .md td {
   padding: 1px 3px;
}

.usertext.border .usertext-body  {
   padding-top: 1px;
   padding-bottom: 1px;
   margin-bottom: -1px;
   margin-top: -1px;
}

.md blockquote, .md del { color: black;}
.md blockquote {
   border-left: 2px solid #369;
   padding-left: 4px;
   margin: 5px;
  }

.usertext-edit textarea { font-size: small; }

.md .-text, .md p, .md pre>code, .md th, .md td, .md li, .usertext-edit textarea .-text, .usertext-edit textarea p, .usertext-edit textarea pre>code, .usertext-edit textarea th, .usertext-edit textarea td, .usertext-edit textarea li {
   font-size: small;
   line-height: normal;
}