*{
  font-family: 
  Avenir, sans-serif;
  color: #222;
  padding: 0px;
}
nav ul{
  display: flex;
  list-style-type: none;
  margin: 0px -10px; 
  /*Expliqué plus loin*/
}

nav ul li{
  flex: 1 1 20%;
  margin: 0px 10px;
  background-color: 
  RGBa(60,120,240,0.1);
}

nav ul li a{
  display: block;
  text-decoration: none;
  color: inherit;
}