nav ul {
  list-style: none;
  background-color: black;
  position:fixed;
  width: 100%;

}

nav ul li {
  float: left;
  margin: 10px;
  font-weight: bolder;

}

nav ul li a {
  color: white;
  text-align: center;
  text-decoration: none;

}
header {
  padding-top: 50px;
}

nav ul {
  list-style: none;
  background-color: black;
  position:fixed;
  width: 100%;

}

nav ul li {
  float: left;
  margin: 10px;
  font-weight: bolder;

}

nav ul li a {
  color: white;
  text-align: center;
  text-decoration: none;

}
header {
  padding-top: 10%;
}

Change header padding to percentage value instead of pixel
Change header padding to percentage value instead of pixel
