Floating Header won't center justify

Hello, I'm trying to a create a simple "coming soon" site to collect email addresses of people interested in a product I'm building. For some reason my floating header is justified left no matter what I try to do to fix it. I have attempted some custom CSS but can't get it to be center justified. I would really appreciate help. The custom code I'm using is in the attached photo and below. 

header {
position: fixed;
left: 0;
right: 0;
margin:4vw;
max-width: 450px;
background-color: rgba(160, 160, 160, .1)!important; 
backdrop-filter: blur(5px)!important;
border-radius: 15px
}

Can you share your website URL?

url: https://cello-heptagon-w47h.squarespace.com/

pw: 1234

wow, thanks so much, that was driving me crazy!

1 minute ago, creativejordan said:

wow, thanks so much, that was driving me crazy!

Happy to find a fix for you!