custom css with ID, can't get working

Trying to get this to work

custom.css:

#thePage body {
  background-color:#999;
  color:#0f0;
}

fck-container html:

//<![CDATA[
CKEDITOR.replace( 'editor1',{
  bodyId : 'thePage',
  contentsCss : 'custom.css',
  ...

Why doesn't it connect? Removing the #thePage shows colours correctly.
Do I need to acivate bodyId with regular js?

Thankful for any working solution based on /_samples
regards,
/t