Look for "css" in the CGI docs (note the 'LIMITED SUPPORT FOR CASCADING STYLE SHEETS' section in the table of contents).. You can tell start_html to have an include for an external css file and/or directly include some css code: 
        start_html(
                -title=>"Foo",
                -style=>{src=>'foo.css', -code=>"body {background-colo
+r: #000000}" },
        ),

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In reply to Re: using a CSS style sheet in CGI by davidrw
in thread using a CSS style sheet in CGI by Anonymous Monk

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