* {
  box-sizing: border-box;
}

@import url(https://fonts.googleapis.com/css?family=PT+Sans);

html, body {
  margin: 0;
  padding: 0;
}

body {
  font-family: Verdana, 'PT Sans', Arial;
  background-color: #eee;
}

h1 {
  text-align: center;
  font-size: 38px;
  text-transform: uppercase;
  letter-spacing: 3px;
  color: #222;
}

.menu {
  list-style: none;
  margin: 0;
  padding: 0;
  width: 100%;
  height: 100px;
  margin: auto;
  position: relative;
  background-color: #2c3e50;
  z-index: 7;
	  li {
		float: left;
		width: 20%;
		height: 100%;
		margin: 0;
		padding: 0;
	  }
  
	  a {
		display: flex;
		width: 100%;
		height: 100%;
		justify-content: center;
		align-items: center;
		color: #fff;
		text-decoration: none;
		position: relative;
		font-size: 18px;
		z-index: 9;
	  }
}

a.active {
  background-color: #e74c3c;
  pointer-events: none;
}

li.slider {
  width: 25%;
  height: 100%;
  position: absolute;
  left: 0;
  top: 0;
  background-color: #e74c3c;
  z-index: 8;
  transition: left .4s, background-color .4s;
}

.menu li:nth-child(1):hover,
.menu li:nth-child(1):focus,
.menu li:nth-child(1):active {
  & ~ .slider {
    left: 0;
    background-color: #3498db;
  }
}


.menu li:nth-child(2):hover,
.menu li:nth-child(2):focus,
.menu li:nth-child(2):active {
  & ~ .slider {
    left: 25%;
    background-color: #9b59b6;
  }
}

.menu li:nth-child(3):hover,
.menu li:nth-child(3):focus,
.menu li:nth-child(3):active {
  & ~ .slider {
    left: 50%;
    background-color: #e67e22;
  }
}

.menu li:nth-child(4):hover,
.menu li:nth-child(4):focus,
.menu li:nth-child(4):active {
  & ~ .slider {
    left: 75%;
    background-color: #16a085;
  }
}