style.css

nav {
  margin: 27px auto 0;

  position: relative;
  width: 590px;
  height: 50px;
  background-color: #34495e;
  border-radius: 8px;
  font-size: 0;
}

nav a {
  line-height: 50px;
  height: 100%;
  font-size: 15px;
  display: inline-block;
  position: relative;
  z-index: 1;
  text-decoration: none;
  text-transform: uppercase;
  text-align: center;
  color: white;
  cursor: pointer;
}

nav .animation {
  position: absolute;
  height: 100%;
  top: 0;
  z-index: 0;
  transition: all .5s ease 0s;
  border-radius: 8px;
}

a:nth-child(1) {
  width: 100px;
}

a:nth-child(2) {
  width: 110px;
}

a:nth-child(3){
  width: 100px;
}

a:nth-child(4){
  width: 160px;
}

a:nth-child(5){
  width: 120px;
}

nav .start-home, a:nth-child(1):hover~.animation {
width: 100px;
left: 0;
background-color: #1abc9c;
}

nav .start-about, a:nth-child(2):hover~.animation {
  width: 110px;
left: 100px;
background-color: #e74c3c;
}

nav .start-blog, a:nth-child(3):hover~.animation {
width: 100px;
left: 210px;
background-color: #3498db;
}

nav .start-portefolio, a:nth-child(4):hover~.animation {
  width: 160px;
  left: 310px;
  background-color: #9b59b6;
}

nav .start-contact, a:nth-child(5):hover~.animation {
  width: 120px;
  left: 470px;
  background-color: #e67e22
}

body {
  font-size: 12px;
  font-family: sans-serif;
  background: #2c3e50;
}

span {
  color: #2bd6b4;
}