CasperJS is not loading full webpage

I'm writing some tests for my website using CasperJS. When I load the webpage in my own browser all items from my HTML and CSS are shown as usual. But when taking a screenshot of my index with CasperJS, almost nothing apears. I posted screenshots below.

This makes my tests fail when I use CasperJS, when everything works fine when I do it by hand.

This is my test code, which fails:

casper.test.begin('Test users without login', 1, function(test) {
// Open the webpage
casper.start('http://localhost:3000', function() {
    // Wait for the website to load
    casper.wait(500, function () {
        // Click the 'Users' button in the upper menu
        casper.capture('screenshot.png'); // SCREENSHOT GETS TAKEN HERE!
        this.click("#users-button");
    }); 
}).viewport(1920,1080);

// Wait for the website to load
casper.wait(500, function () {
    // Are you on the right page? 
    test.assertUrlMatch('http://localhost:3000/ratings.html'); // RESULT = localhost:3000/
 }); 
 // Run the test
 casper.run(function() {
     test.done();
 });
 })

Screenshot taken by CasperJS

Screenshot taken in own browser

It doesn't matter how long I wait for the page to load, it keeps almost empty.

Hope someone could help.