.menu {
  list-style-type: none;
  padding: 0;
  margin: 0;
}

.menu > li {
  position: relative;
}

.menu > li > a {
  display: block;
  padding: 10px 15px;
  text-decoration: none;
  background-color: #555;
  color: white;
  border-radius:10px;
}

.menu > li > a:hover {
  background-color: #777;
}

.submenu {
  list-style-type: none;
  padding: 0;
  margin: 0;
  position: absolute;
  top: 100%;
  left: 0;
  display: none;
  background-color: #666;
  z-index: 1000; /* 最前面に表示するためのz-index */
}

.submenu > li > a {
  display: block;
  padding: 10px 15px;
  text-decoration: none;
  color: white;
}

.submenu > li > a:hover {
  background-color: #444;
}

.menu > li:hover .submenu {
  display: block;
}