Your nav-bar should always be at the top of the viewport

HTML-CSS
9

To solve this task you have to specify all of the axis positions (top, right, bottom, left) of the section you set the positioning. In this case it was the header, so you need to set as the following:

header {
    position: fixed;
    width: 100%;
/*Axis positions*/
    top: 0;
    left: 0;
    right: 0;
    bottom: 0;
/*Axis positions*/
    min-height: 75px;
    background-color: rgb(255, 255, 255);
    display: flex;
    justify-content: space-around;
    align-items: center;
    padding: 1em;
}

I set all of them as 0, but of course you should set it as what is best for you.
You an check the solution in my topic as well #nav-bar at the top of viewport - #4 by joaovinicius1234576