I did
perl -MCGI index.cgi > test.html
this is index.cgi

#!/usr/bin/perl -w

use strict;
use diagnostics;

use CGI;
use CGI::Carp qw(fatalsToBrowser warningsToBrowser);
use CGI::Pretty;

use DBI;

warningsToBrowser(1);

my $q = CGI->new();
my $title = "mt Annotation pipeline";


print $q->header(),

      $q -> start_html(-title => "$title",
                        -style => { -src => 'mycss/mtannot.css', -type
+ => 'text/css', -media => 'screen' }),
      
      $q->div({-class=>"header"},$title),
      $q->div({-style=>"float: left"},
        $q->div({-class=>"menu"},
          $q->h3("menu"),
          ("here is some text"),
          $q->br(),
          ("spanning two lines")
        ),
      ),
     $q->div({-class=>"content"},
              $q->h1('First Upload your sequence'),        
              $q->table ( {bgColor=> "blue", -border=>1},
                $q->TR([
                  $q->td("1") . $q->td("A") . $q->td("2") . $q->td("B"
+),
                ]),
                $q->TR([
                  $q->td("1") . $q->td("A") . $q->td("2") . $q->td("B"
+),
                ]),
              ),
          ),

     $q -> end_html();
[download]

and this is the css file:

BODY {
  background-color: #0e7aef;
  color: white; 
  font-family: sans-serif;
  background: url(images/vbc.jpg) no-repeat fixed top right;
}

LI {
  margin-bottom: 1ex;
}

H1 {
  color:black;
}

.header {
  font-size: 4em;
  border: solid thin black;
  background-color: #8B475D;
  text-align: center;
  padding-top: 0px;
  margin: 0px 0px 10px 0px;
  color: #7FFF00;
  width: 90%;
}

.content {
  margin-left: 16em;

  padding: 1em 1em 1em 1em;

  background-color: #eee;
  border: solid thin black;
  width: 75%;
}

.menu {
  background-color: #b3d5ff;
  width: 15em;
  border: solid thin black;
  text-align: center;
  color: black;
}
[download]

How do you change the body' background-color in your css?