* {
  margin: 0;
  padding: 0;
  box-sizing: border-box;
}

body {
  font-family: Arial, sans-serif;
  background-color: whitesmoke;
}

.navbar {
  background: #000;
  display: flex;
  list-style: none;
}

.navbar li {
  position: relative;
}

.navbar li a {
  color: white;
  padding: 15px 20px;
  text-decoration: none;
  display: block;
}

.navbar li a:hover {
  background: #fff;
  color: #000;
}

.dropdown-content {
  position: absolute;
  top: 100%;
  left: 0;
  background: #000;
  opacity: 0;
}

.dropdown:hover .dropdown-content {
  opacity: 1;
  visibility: visible;
}
.dropdown-content li {
  list-style: none;
}

.main {
  padding: 20px;
  margin-top: 20px;
}

.dropdown-sub {
  position: relative;
}

.dropdown-sub-content {
  display: none;
  position: absolute;
  left: 100%;          
  top: 0;
  background: #000;    
  min-width: 160px;
  z-index: 1001;      
}

.dropdown-sub:hover .dropdown-sub-content {
  display: block;
}

.dropdown-sub-content a:hover {
  background: #555;
}