index.css

* {
    margin: 0;
    padding: 0;
    box-sizing: border-box;
    font-family: sans-serif;
  }
  
  nav {
    width: 100%;
    height: 70px;
    display: flex;
    justify-content: space-between;
    align-items: center;
    padding-inline: 3em;
    position: fixed;
    top: 0;
    left: 0;
  }
  
  nav ul {
    display: flex;
    gap: 2em;
    list-style: none;
  }
  
  nav ul li {
    opacity: .8;
    cursor: pointer;
  }
  
  nav ul li:hover {
    opacity: 1;
  }
  
  nav button {
    position: relative;
    width: 25px;
    height: 25px;
    background: transparent;
    outline: none;
    border: none;
  }
  
  nav button span {
    width: 100%;
    height: 5px;
    background: black;
    position: absolute;
    border-radius: 1em;
    transition: .3s;
  }
  nav button span:nth-of-type(1) {
    top: 0;
    left: 0;
    box-shadow: 0px 10px 0 black;
  }
  nav button span:nth-of-type(2) {
    bottom: 0;
    left: 0;
  }
  
  @media (min-width: 768px) {
    nav button {
      display: none;
    }
  }
  
  @media (max-width: 768px) {
    nav ul {
      position: absolute;
      top: 70px;
      right: 0;
      width: 100%;
      height: calc(100vh - 70px);
      background: #ccc;
      flex-direction: column;
      align-items: flex-end;
      padding: 2em 5em;
      transform: translateX(100%);
      transition: .3s;
    }
    
    nav button:focus ~ ul {
      transform: translateX(0%);
    }
    
    nav button:focus span {
      box-shadow: none;
      transform: rotate(40deg) translateY(13px);
    }
    
    nav button:focus span:nth-of-type(2) {
      transform: rotate(-40deg) translateY(-13px);
    }
  }