The image is not getting ... well positioned. What do I do ? You have that space. It's for her ... she's behind the menu. Without getting that white line dividing the two.
* { margin: 0; padding: 0; }
nav {
position: fixed;
width: 100%;
height: 70px;
background: blue;
z-index: 999;
}
header {
width: 100%;
height: 500px;
background: red;
}
<nav>Menu</nav>
<header>imagem</header>
If you do not want to leave the menu fixed at the top, take the position.