HTML+CSS3+JS 实现的下拉菜单

<div class="container">
  <h1 class="title">Dropdown Menu</h1>
  <ul>
    <li class="dropdown">
      <a href="#" data-toggle="dropdown">First Menu <i class="icon-arrow"></i></a>
      <ul class="dropdown-menu">
        <li><a href="#">Home</a></li>
        <li><a href="#">About Us</a></li>
        <li><a href="#">Services</a></li>
        <li><a href="#">Contact</a></li>
      </ul>
    </li>
    <li class="dropdown">
      <a href="#" data-toggle="dropdown">Second Menu <i class="icon-arrow"></i></a>
      <ul class="dropdown-menu">
        <li><a href="#">Home</a></li>
        <li><a href="#">About Us</a></li>
        <li><a href="#">Services</a></li>
        <li><a href="#">Contact</a></li>
      </ul>
    </li>
    <li class="dropdown">
      <a href="#" data-toggle="dropdown">Third Menu <i class="icon-arrow"></i></a>
      <ul class="dropdown-menu">
        <li><a href="#">Home</a></li>
        <li><a href="#">About Us</a></li>
        <li><a href="#">Services</a></li>
        <li><a href="#">Contact</a></li>
      </ul>
    </li>
  </ul>
  <p class="text-center">
    See this same menu only with CSS3: <a href="https://codepen.io/pedronauck/pen/jaluz" target="_blank">https://codepen.io/pedronauck/pen/jaluz</a>
  </p>
</div>

@import url("https://fonts.googleapis.com/css?family=Lato:300,400,700,900");
@import url(https://fonts.googleapis.com/css?family=Pacifico);
body {
  font-family: "Lato", Helvetica, Arial;
  font-size: 16px;
}

.text-center {
  text-align: center;
}

*, *:before, *:after {
  -webkit-border-sizing: border-box;
  -moz-border-sizing: border-box;
  border-sizing: border-box;
}

.container {
  width: 350px;
  margin: 50px auto;
}
.container > ul {
  list-style: none;
  padding: 0;
  margin: 0 0 20px 0;
}

.title {
  font-family: 'Pacifico';
  font-weight: norma;
  font-size: 40px;
  text-align: center;
  line-height: 1.4;
  color: #2980B9;
}

.dropdown a {
  text-decoration: none;
}
.dropdown [data-toggle="dropdown"] {
  position: relative;
  display: block;
  color: white;
  background: #2980B9;
  -moz-box-shadow: 0 1px 0 #409ad5 inset, 0 -1px 0 #20638f inset;
  -webkit-box-shadow: 0 1px 0 #409ad5 inset, 0 -1px 0 #20638f inset;
  box-shadow: 0 1px 0 #409ad5 inset, 0 -1px 0 #20638f inset;
  text-shadow: 0 -1px 0 rgba(0, 0, 0, 0.3);
  padding: 10px;
}
.dropdown [data-toggle="dropdown"]:hover {
  background: #2c89c6;
}
.dropdown .icon-arrow {
  position: absolute;
  display: block;
  font-size: 0.7em;
  color: #fff;
  top: 14px;
  right: 10px;
}
.dropdown .icon-arrow.open {
  -moz-transform: rotate(-180deg);
  -ms-transform: rotate(-180deg);
  -webkit-transform: rotate(-180deg);
  transform: rotate(-180deg);
  -moz-transition: -moz-transform 0.6s;
  -o-transition: -o-transform 0.6s;
  -webkit-transition: -webkit-transform 0.6s;
  transition: transform 0.6s;
}
.dropdown .icon-arrow.close {
  -moz-transform: rotate(0deg);
  -ms-transform: rotate(0deg);
  -webkit-transform: rotate(0deg);
  transform: rotate(0deg);
  -moz-transition: -moz-transform 0.6s;
  -o-transition: -o-transform 0.6s;
  -webkit-transition: -webkit-transform 0.6s;
  transition: transform 0.6s;
}
.dropdown .icon-arrow:before {
  content: '\25BC';
}
.dropdown .dropdown-menu {
  max-height: 0;
  overflow: hidden;
  list-style: none;
  padding: 0;
  margin: 0;
}
.dropdown .dropdown-menu li {
  padding: 0;
}
.dropdown .dropdown-menu li a {
  display: block;
  color: #6f6f6f;
  background: #EEE;
  -moz-box-shadow: 0 1px 0 white inset, 0 -1px 0 #d5d5d5 inset;
  -webkit-box-shadow: 0 1px 0 white inset, 0 -1px 0 #d5d5d5 inset;
  box-shadow: 0 1px 0 white inset, 0 -1px 0 #d5d5d5 inset;
  text-shadow: 0 -1px 0 rgba(255, 255, 255, 0.3);
  padding: 10px 10px;
}
.dropdown .dropdown-menu li a:hover {
  background: #f6f6f6;
}
.dropdown .show, .dropdown .hide {
  -moz-transform-origin: 50% 0%;
  -ms-transform-origin: 50% 0%;
  -webkit-transform-origin: 50% 0%;
  transform-origin: 50% 0%;
}
.dropdown .show {
  display: block;
  max-height: 9999px;
  -moz-transform: scaleY(1);
  -ms-transform: scaleY(1);
  -webkit-transform: scaleY(1);
  transform: scaleY(1);
  animation: showAnimation 0.5s ease-in-out;
  -moz-animation: showAnimation 0.5s ease-in-out;
  -webkit-animation: showAnimation 0.5s ease-in-out;
  -moz-transition: max-height 1s ease-in-out;
  -o-transition: max-height 1s ease-in-out;
  -webkit-transition: max-height 1s ease-in-out;
  transition: max-height 1s ease-in-out;
}
.dropdown .hide {
  max-height: 0;
  -moz-transform: scaleY(0);
  -ms-transform: scaleY(0);
  -webkit-transform: scaleY(0);
  transform: scaleY(0);
  animation: hideAnimation 0.4s ease-out;
  -moz-animation: hideAnimation 0.4s ease-out;
  -webkit-animation: hideAnimation 0.4s ease-out;
  -moz-transition: max-height 0.6s ease-out;
  -o-transition: max-height 0.6s ease-out;
  -webkit-transition: max-height 0.6s ease-out;
  transition: max-height 0.6s ease-out;
}

@keyframes showAnimation {
  0% {
    -moz-transform: scaleY(0.1);
    -ms-transform: scaleY(0.1);
    -webkit-transform: scaleY(0.1);
    transform: scaleY(0.1);
  }
  40% {
    -moz-transform: scaleY(1.04);
    -ms-transform: scaleY(1.04);
    -webkit-transform: scaleY(1.04);
    transform: scaleY(1.04);
  }
  60% {
    -moz-transform: scaleY(0.98);
    -ms-transform: scaleY(0.98);
    -webkit-transform: scaleY(0.98);
    transform: scaleY(0.98);
  }
  80% {
    -moz-transform: scaleY(1.04);
    -ms-transform: scaleY(1.04);
    -webkit-transform: scaleY(1.04);
    transform: scaleY(1.04);
  }
  100% {
    -moz-transform: scaleY(0.98);
    -ms-transform: scaleY(0.98);
    -webkit-transform: scaleY(0.98);
    transform: scaleY(0.98);
  }
  80% {
    -moz-transform: scaleY(1.02);
    -ms-transform: scaleY(1.02);
    -webkit-transform: scaleY(1.02);
    transform: scaleY(1.02);
  }
  100% {
    -moz-transform: scaleY(1);
    -ms-transform: scaleY(1);
    -webkit-transform: scaleY(1);
    transform: scaleY(1);
  }
}
@-moz-keyframes showAnimation {
  0% {
    -moz-transform: scaleY(0.1);
    -ms-transform: scaleY(0.1);
    -webkit-transform: scaleY(0.1);
    transform: scaleY(0.1);
  }
  40% {
    -moz-transform: scaleY(1.04);
    -ms-transform: scaleY(1.04);
    -webkit-transform: scaleY(1.04);
    transform: scaleY(1.04);
  }
  60% {
    -moz-transform: scaleY(0.98);
    -ms-transform: scaleY(0.98);
    -webkit-transform: scaleY(0.98);
    transform: scaleY(0.98);
  }
  80% {
    -moz-transform: scaleY(1.04);
    -ms-transform: scaleY(1.04);
    -webkit-transform: scaleY(1.04);
    transform: scaleY(1.04);
  }
  100% {
    -moz-transform: scaleY(0.98);
    -ms-transform: scaleY(0.98);
    -webkit-transform: scaleY(0.98);
    transform: scaleY(0.98);
  }
  80% {
    -moz-transform: scaleY(1.02);
    -ms-transform: scaleY(1.02);
    -webkit-transform: scaleY(1.02);
    transform: scaleY(1.02);
  }
  100% {
    -moz-transform: scaleY(1);
    -ms-transform: scaleY(1);
    -webkit-transform: scaleY(1);
    transform: scaleY(1);
  }
}
@-webkit-keyframes showAnimation {
  0% {
    -moz-transform: scaleY(0.1);
    -ms-transform: scaleY(0.1);
    -webkit-transform: scaleY(0.1);
    transform: scaleY(0.1);
  }
  40% {
    -moz-transform: scaleY(1.04);
    -ms-transform: scaleY(1.04);
    -webkit-transform: scaleY(1.04);
    transform: scaleY(1.04);
  }
  60% {
    -moz-transform: scaleY(0.98);
    -ms-transform: scaleY(0.98);
    -webkit-transform: scaleY(0.98);
    transform: scaleY(0.98);
  }
  80% {
    -moz-transform: scaleY(1.04);
    -ms-transform: scaleY(1.04);
    -webkit-transform: scaleY(1.04);
    transform: scaleY(1.04);
  }
  100% {
    -moz-transform: scaleY(0.98);
    -ms-transform: scaleY(0.98);
    -webkit-transform: scaleY(0.98);
    transform: scaleY(0.98);
  }
  80% {
    -moz-transform: scaleY(1.02);
    -ms-transform: scaleY(1.02);
    -webkit-transform: scaleY(1.02);
    transform: scaleY(1.02);
  }
  100% {
    -moz-transform: scaleY(1);
    -ms-transform: scaleY(1);
    -webkit-transform: scaleY(1);
    transform: scaleY(1);
  }
}
@keyframes hideAnimation {
  0% {
    -moz-transform: scaleY(1);
    -ms-transform: scaleY(1);
    -webkit-transform: scaleY(1);
    transform: scaleY(1);
  }
  60% {
    -moz-transform: scaleY(0.98);
    -ms-transform: scaleY(0.98);
    -webkit-transform: scaleY(0.98);
    transform: scaleY(0.98);
  }
  80% {
    -moz-transform: scaleY(1.02);
    -ms-transform: scaleY(1.02);
    -webkit-transform: scaleY(1.02);
    transform: scaleY(1.02);
  }
  100% {
    -moz-transform: scaleY(0);
    -ms-transform: scaleY(0);
    -webkit-transform: scaleY(0);
    transform: scaleY(0);
  }
}
@-moz-keyframes hideAnimation {
  0% {
    -moz-transform: scaleY(1);
    -ms-transform: scaleY(1);
    -webkit-transform: scaleY(1);
    transform: scaleY(1);
  }
  60% {
    -moz-transform: scaleY(0.98);
    -ms-transform: scaleY(0.98);
    -webkit-transform: scaleY(0.98);
    transform: scaleY(0.98);
  }
  80% {
    -moz-transform: scaleY(1.02);
    -ms-transform: scaleY(1.02);
    -webkit-transform: scaleY(1.02);
    transform: scaleY(1.02);
  }
  100% {
    -moz-transform: scaleY(0);
    -ms-transform: scaleY(0);
    -webkit-transform: scaleY(0);
    transform: scaleY(0);
  }
}
@-webkit-keyframes hideAnimation {
  0% {
    -moz-transform: scaleY(1);
    -ms-transform: scaleY(1);
    -webkit-transform: scaleY(1);
    transform: scaleY(1);
  }
  60% {
    -moz-transform: scaleY(0.98);
    -ms-transform: scaleY(0.98);
    -webkit-transform: scaleY(0.98);
    transform: scaleY(0.98);
  }
  80% {
    -moz-transform: scaleY(1.02);
    -ms-transform: scaleY(1.02);
    -webkit-transform: scaleY(1.02);
    transform: scaleY(1.02);
  }
  100% {
    -moz-transform: scaleY(0);
    -ms-transform: scaleY(0);
    -webkit-transform: scaleY(0);
    transform: scaleY(0);
  }
}

// Dropdown Menu
var dropdown = document.querySelectorAll('.dropdown');
var dropdownArray = Array.prototype.slice.call(dropdown,0);
dropdownArray.forEach(function(el){
	var button = el.querySelector('a[data-toggle="dropdown"]'),
			menu = el.querySelector('.dropdown-menu'),
			arrow = button.querySelector('i.icon-arrow');

	button.onclick = function(event) {
		if(!menu.hasClass('show')) {
			menu.classList.add('show');
			menu.classList.remove('hide');
			arrow.classList.add('open');
			arrow.classList.remove('close');
			event.preventDefault();
		}
		else {
			menu.classList.remove('show');
			menu.classList.add('hide');
			arrow.classList.remove('open');
			arrow.classList.add('close');
			event.preventDefault();
		}
	};
})

Element.prototype.hasClass = function(className) {
    return this.className && new RegExp("(^|\\s)" + className + "(\\s|$)").test(this.className);
};