[shaahin]

I must add
this

h3 {
  string-set: chaptertitle content();
}

in body section

and
this

  @top-center {
    font-size: 50%;
    font-style: italic;
    border-bottom: solid thin black;
    margin-bottom: 1mm;
    content: string(chaptertitle);
  }

to plugin like this

/*
@font-face {
  font-family: serif;
  src: local("Droid Serif")
}
*/

@page {
  size: 9cm 12cm;
  margin: 5mm 1mm 1mm 1mm !important;
  @top-left {
    font-size: 50%;
    font-style: italic;
    border-bottom: solid thin black;
    margin-bottom: 1mm;
    content: string(booktitle);
  }
  @top-center {
    font-size: 50%;
    font-style: italic;
    border-bottom: solid thin black;
    margin-bottom: 1mm;
    content: string(chaptertitle);
  }
  @top-right {
    font-size: 50%;
    border-bottom: solid thin black;
    margin-bottom: 1mm;
    content: counter(page) "/" counter(pages);
  }
}

@page:first {
  margin: 1mm 1mm 1mm 1mm;
  @top-left {
    border-width: 0;
    margin: 0;
    content: normal;
  }
  @top-center {
    border-width: 0;
    margin: 0;
    content: normal;
  }
  @top-right {
    border-width: 0;
    margin: 0;
    content: normal;
  }
}

body {
  font-size: 10pt;
  font-family: serif;
  text-align: justify;
  prince-image-resolution: 166dpi;
  hyphens: auto;
  string-set: booktitle "@{@{title}@}@"
  string-set: author "@{@{author}@}@"
  h3 {
  string-set: chaptertitle content();
}
}