Page is different in codepen

I’m using visual studio to write my code, but when I copy & paste to codepen nothing works. I have added bootstrap to codepen but still not sure why. first pic is codepen. second is what it looks like opened in chrome. Any suggestion?

Codepen can not access any files stored on your local computer. That is why the following will not work:

<link rel="stylesheet" type="text/css" href="C:\Users\David\Documents\Web Design\Personal Portfolio\css\styles.css">

and also why the CSS like below will not work:

.jumbotronimg {
  background-image: url("../img/greg-rakozy-vw3Ahg4x1tY-unsplash.jpg");
  background-size: cover;
  min-height: 1000px;
  max-width: 100%;
}

oh i see. sorry but what would be the proper way to link the css?

Put all the HTML between the body tags in the HTML window. Need to put stuff in the document head? Click the gear icon in the HTML window. Put all the CSS in the CSS window. Need CSS libraries or frameworks? Link to them by clicking the gear icon in the CSS window.