<div class="container">
  <input type="checkbox" id="toggle" checked />
  <label class="button" for="toggle">
    <nav class="nav">
      <ul>
        <li><a href="#0"><i class="ri-mic-line"></i></a></li>
        <li><a href="#0"><i class="ri-message-2-line"></i></a></li>
        <li><a href="#0"><i class="ri-file-line"></i></a></li>
        <li><a href="#0"><i class="ri-send-plane-2-line"></i></a></li>
      </ul>
    </nav>
  </label>
</div>

$darkbg: #1c1c1c;
$btCinza: #222;
$icons: #eeff00;
$branco: #fff;

* {
  box-sizing: border-box;
  margin: 0;
  padding: 0;
}

body {
  background: $darkbg;
  display: flex;
  justify-content: center;
  align-items: center;
  height: 100vh;
}
.container {
  width: 20%;
  display: flex;
  justify-content: left;
  align-items: center;
  position: relative;
}

#toggle {
  -webkit-appearance: none;
}

.button {
  position: absolute;
  z-index: 999;
  width: 320px;
  height: 65px;
  background: $btCinza;
  border-radius: 15px;
  cursor: pointer;
  display: flex;
  justify-content: left;
  align-items: center;
  padding: 0 24px;
  overflow: hidden;
  transition: width 300ms linear;

  &:before {
    position: absolute;
    content: "";
    width: 20px;
    height: 2px;
    background: $icons;
    transform: rotate(225deg);
    transition: all 0.4s ease;
  }
  &:after {
    position: absolute;
    content: "";
    width: 20px;
    height: 2px;
    background: $icons;
    transform: rotate(135deg);
    transition: all 0.4s ease;
  }
}

.nav {
  opacity: 1;
  transition: all 0.5s ease-in-out;
  background: $btCinza;
  width: 100%;
  border-radius: 5px;
  transform: translateX(10%);
  padding: 10px;

  ul {
    margin: 0;
    padding: 0;
    display: flex;
    flex-direction: row;
  }
  li {
    opacity: 0;
    list-style: none;
    &:nth-child(1) {
      transform-origin: bottom;
      animation: itop 300ms 300ms linear forwards;
    }
    &:nth-child(2) {
      transform-origin: bottom;
      animation: itop 300ms 400ms linear forwards;
    }
    &:nth-child(3) {
      transform-origin: bottom;
      animation: itop 300ms 500ms linear forwards;
    }
    &:nth-child(4) {
      transform-origin: bottom;
      animation: itop 300ms 600ms linear forwards;
    }
  }
  a {
    transition: all 0.5s linear;
    text-decoration: none;
    color: #eeff00;
    font-size: 20px;
    width: 52px;
    height: 52px;
    display: flex;
    align-items: center;
    justify-content: center;
    margin: 0 10px 0 0;
    border-radius: 15px;

    &:hover {
      color: $branco;
      background: $darkbg;
      border-radius: 15px;
    }
  }
}

#toggle:checked ~ label .nav {
  display: none;
  opacity: 0;
  transform: translateX(0);
}

#toggle:checked ~ .button:before {
  transform: rotate(90deg);
}

#toggle:checked ~ .button:after {
  transform: rotate(0deg);
}

#toggle:checked ~ .button {
  width: 70px;
  transition: all 0.1s linear;
}

@media (max-width: 640px) {
  .container {
    width: 100%;
  }
}

@keyframes itop {
  0% {
    opacity: 0;
    transform: translateY(60px);
  }
  100% {
    opacity: 1;
    transform: translateY(0);
  }
}