*,
*::before,
*::after {
  margin: 0;
  padding: 0;
}

body {
  background: url("../images/background.jpg") no-repeat;
  background-size: cover;
  color: white;
}

header {
  font-family: verdana
}

header nav {
  display: flex;
  justify-content: center;
  align-items: center;
}

header nav ul li {
  margin: 0;
  padding: 0;
  float: left;
  width: 180px;
  height: 40px;
  background-color: rgba(0, 0, 0, 0.8);
  line-height: 40px;
  text-align: center;
  list-style: none;
}

header nav ul li a {
  display: block;
  color: inherit;
  text-decoration: none;
}

header nav ul li a:hover {
  background-color: grey;
  opacity: 0.5;
}

header nav ul li ul li {
  display: none;
}

header nav ul li:hover ul li {
  display: block;
}