Print the contents of div with css

Question

I got it with the help of Stackoverflow assemble a script for printing a document, now I’m with a second problem, the script opens the print page without formatting the css. I saw an example right here but could not change according to what I need, I saw it here:

Example of css being loaded

In the example css is being loaded by script, but in my example I have this:

document.getElementById('btn').onclick = function() {   
    var conteudo = document.getElementById('conteudo').innerHTML,
    impressao = window.open('about:blank');
    impressao.document.write(conteudo);
    impressao.window.print();
    impressao.window.close();
};

How can I load css in my example?