Chris,

If you want the header to show up on the completed Form, then you need to use Custom HTML elements and CSS. Anything added through JavaScript won't stay on the Form after it is saved to the repository and might also cause problems when viewing the form for approvals.

Instead, I would recommend using "position:absolute;" on your Custom HTML element to get it where you want it

div#<Id of your custom element>{
   position:absolute;
   top:0;
}

then, push the rest of the form down as much as you need

div.cf-formwrap {
   margin-top:200px;
}

However, if you want to have your custom image within the curved border you will need to get fancier. In that case you would need to pad the top of the Title element (div#cf-formtitle) to make room for the image instead of shifting the entire form down.

As Rui mentioned, in that case you could just upload a Logo to Forms and apply that to the form. Even if it is not exactly where you want it you could use CSS to shift things around as needed, and that would be far more effective and reliable than JavaScript.