header.php

<!--menu wp-->
<nav>
<ul class="dropdown"><li>
<?php wp_nav_menu( array( 'theme_location' => 'primary', 'menu_class' => 'nav-menu' ) ); ?>
</li></ul></nav>

<!--menu wp-->
<script>
$(function() { 
// Dropdown toggle
$('.dropdown-toggle').click(function(){
  $(this).next('.dropdown').toggle();
});
$(document).click(function(e) {
  var target = e.target;
  if (!$(target).is('.dropdown-toggle') && !$(target).parents().is('.dropdown-toggle')) {
    $('.dropdown').hide();
  }
});
});
</script>

style.css

nav {
  position: relative;
}
.dropdown-toggle {
  padding: .5em 1em;
  background: #777;
  border-radius: .2em .2em 0 0;
}
ul.dropdown {
  display:none;
  position: absolute;
  top: 100%;
  margin-top: .5em;
  background: #777;
  min-width: 12em;
  padding: 0;
  border-radius: 0 0 .2em .2em;
    li {
      list-style-type: none;
      a {
        text-decoration: none;
        padding: .5em 1em;
        display: block;
      }
   }
}