.nav-menu {
  display: flex;
  flex-flow: row wrap;
  background: #333;
  padding: 0;
  margin: 0;
  list-style: none;
  border-radius: 4px;
}

.nav-menu li {
  flex: 1 1 auto;
}

.nav-menu a {
  display: block;
  padding: 15px 20px;
  color: white;
  text-decoration: none;
  text-align: center;
  border-right: 1px solid #555;
  transition: background-color 0.3s;
}

.nav-menu a:hover {
  background-color: #555;
}

.nav-menu li:last-child a {
  border-right: none;
}