header.css

* {
  margin: 0;
  padding: 0;
  box-sizing: border-box;
}
body{
  height: 3000px;
}
nav {
  position: fixed;
  display: flex;
  justify-content: space-evenly;
  align-items: center;
  width:100%;
  height: 10%;
  background: #fff;
  border-radius: 0 0 20px 20px;
  border:1px solid rgba(0, 0, 0, 0.2);
  border-top: none;
  box-shadow: 0 25px 10px -25px rgba(0, 0, 0, 0.4);
}
nav>ul{
  display: flex;
  justify-content: space-evenly;
  align-items: center;
  flex-basis: 60%;
}
nav #menu-button{
  display: none;
}
nav .menu-button{
  display: none;
}
nav>ul>li {
  width: 20%;
  list-style: none;
  padding: 10px;
  font-size: 20px;
  font-weight: 500;
  color: #777;
  cursor: pointer;
  position: relative;
  z-index: 2;
  transition: color 0.5s;
  text-align: center;
}
nav>ul>li::after {
  content: '';
  background: #FF8066;
  width: 10%;
  height: 10%;
  border-radius: 20px;
  position: absolute;
  top: 50%;
  left: 50%;
  transform: translate(-50%, -50%);
  z-index: -1;
  opacity: 0;
  transition: all 0.4s ease-out;
}
nav>ul>li:hover{
  color: #fff;
}
nav>ul>li:hover::after{
  width: 70%;
  height: 100%;
  opacity: 1;
}
@media screen and (max-width:768px){
  nav {
    position: fixed;
    display: inline-block;
  }
  nav .menu-button{
    display: inline-block;
    position: absolute;
    top: 50%;
    left: 50%;
    cursor: pointer;
    transform: translate(-50%,-50%);
  }
  nav>ul{
    display: flex;
    position: absolute;
    top: -300%;
    left: 50%;
    transform: translateX(-50%);
    flex-direction: column;
    border-radius: 0 0 5px 5px;
    border:1px solid rgba(0, 0, 0, 0.2);
    border-top: none;
    opacity: 0;
    transition: all 0.4s ease-out;
  }
  nav>ul>li {
    width: 100%;
  }
  nav>ul>li:hover::after{
    width: 100%;
    height: 80%;
    opacity: 1;
  }
  nav>div{
    display: inline-block;
    position: absolute;
    top: 50%;
    transform: translateY(-50%);
  }
  nav #logo{
    left: 20px;
  }
  nav #nav-user-link{
    right: 20px;
  }
  nav #menu-button:checked ~ #nav-menu{
    top: 100%;
    opacity: 1;
  }
}