If you inspect the elements using the browser tools you will see there is a 21.4px
top-margin
on your headerExperience
element. You can add a reset to your css to reset all margin and padding to 0. Then if you desire margin and/or padding you can add as needed directly to the elements you want.
*{
margin: 0;
padding: 0;
}
*{
margin: 0;
padding: 0;
box-sizing: border-box;
}
html {
background-color: #9bf6ff;
font-family: 'Oswald', sans-serif;
width: auto;
}
#headerExperience {
line-height: 200px;
font-family: "proxima nova bold", "Helvetica Neue", Helvetica, Arial, sans-serif;
color: khaki;
background-color: steelblue;
background-image: url("images/Experience\ background\ imagee.jpg");
background-size: cover;
background-position: center;
background-repeat: no-repeat;
text-align: center;
}
<html>
<!--Header-->
<div id="headerExperience">
<h1>Experience</h1>
</div>
</html>