position: top, @Tirjasdyn did not mean that.
You have to use position property with value as
position: fixed and then make it to
top: 0; left: 0; and apply a
You have given the
position: fixed thats fine, now give it a
left property as in the above hint and give it a
100% width, now you will be able to see your navbar on top.
ul tag there will be a default
padding, so you have to clear it out and adjust it according to your need.
flex properties to
header to make the elements in your navbar to align center.