How to center Header tag?

Question

I have 1440px window and set max-width = 800px

HTML CODE:
<header>
<h1>Hi Hello!</h1>
<div>
<ul>
<li><a href="#" >Home</a></li>
<li><a href="#" >About</a></li>
<li><a href="#" >Contact</a></li>
</ul>
</div>
</header>

CSS CODE:
header {
position: fixed;
top: 0;
width: 100%;
max-width: 800px;
}

Answer 1

Surya Magesh add both rules to header css:

left:50%;
transform:translateX(-50%);

Answer 2

.header {
Position : absolute;
justify-items : center:
}