Getting error message I don't understand

Ok so I've followed all the tutorials I can. I'm trying to create a header picture at the top of my journal. I don't want it to change my lay-out or my colors, I just want a picture on top.

I went to the Advanced Customization page and created a layout-specific layer. I clicked edit on my new layer and in the box to "compile" I wrote the code I was told to in tutorials, with my specifications ofcourse. When I clicked the compile button this error message showed. I don't understand it.

Compile error: line 4, column 1: Can't declare function page::print_custom_head() for non-existent class 'page'
  S2::NodeFunction, S2/NodeFunction.pm, 159
  S2::Checker, S2/Checker.pm, 339
  S2::Compiler, S2/Compiler.pm, 34
  

  1: layerinfo "type" = "theme";
  2: layerinfo "name" = "tara singing spell";
  3: 
  4: function page::print_custom_head() {
  5:    """
  6:    <style type="text/css">
  7:      body {
  8:       background-image: url(http://usera.imagecave.com/seiramnomad/1stbannorforlj.jpg) ;

This was the code I placed in the box......

layerinfo "type" = "theme";
layerinfo "name" = "tara singing spell";

function page::print_custom_head() {
   """
   <style type="text/css">
     body {
      background-image: url(http://usera.imagecave.com/seiramnomad/1stbannorforlj.jpg) ;
      background-repeat: no-repeat ;
      background-attachment: fixed ;
      background-position: top ;
      margin-top: 350px ;
     }
   </style>
   """;
 }

What do I do? Thanks