Formatting Header To Include Form

Hi,
I’ve been pulling my hair out for weeks trying to figure out how to embed a form in my blog header image, like this:

https://jianiteo.com/

When I contacted the website’s owner she said that it’s coding.

I’m not an expert programmer however I’ve tried this coding previously posted in the forum however it adds the form above or below my header image even when I add coding to the CSS to reposition it:

<div id="header" class="clearfix">
<div class='aweberForm'>
<script type="text/javascript" src="https://forms.aweber.com/form/81/915320281.js"></script>
</div>

CSS

#header {
background:transparent url(https://guitarstuffreviewed.com/wp-content/themes/Bravo/images/header.jpg) no-repeat scroll left top;
height:145px;
width:960px;
position: relative;}

div.aweberForm { position: absolute; top: 50px; left: 400px; }

Is there another coding format I can use to get the exact result I’m after? Would really appreciate it.

Thank You