style.css

html,
body {
  height: 100%;
  width: 100%;
  overflow: hidden;
  padding: 0;
  margin: 0;
  font-family: Arial, Helvetica, sans-serif;
}
body {
  background: #272b33;
}
* {
  position: absolute;
}

.container {
  top: 50%;
  left: 50%;
  transform: translate(-50%, -50%);
  height: 400px;
  width: 400px;
}

button {
  top: 50%;
  left: 50%;
  transform: translate(-50%, -50%);
  position: relative;
  border: none;
  outline: none;
  background: none;
  height: 30px;
  width: 30px;
  cursor: pointer;
  -webkit-tap-highlight-color: rgba(255, 255, 255, 0);
}

.left {
  height: 2px;
  width: 30px;
  background-color: white;
  transition: all 300ms ease-in-out;
}

.left::after {
  position: absolute;
  height: 2px;
  width: 16px;
  background-color: white;
  content: "";
  left: -3px;
  top: -5px;
  transform: rotate(-45deg);
  transition: all 300ms ease-in-out;
}

.left::before {
  position: absolute;
  height: 2px;
  width: 16px;
  background-color: white;
  content: "";
  left: -3px;
  bottom: -5px;
  transform: rotate(-135deg);
  transition: all 300ms ease-in-out;
}

.changeToCross {
  transform: rotate(-45deg);
}

.changeToCross::after {
  width: 16px;
  transform: rotate(-90deg);
  left: 6px;
  top: -8px;
  transition: all 300ms ease-in-out;
}

.changeToCross::before {
  width: 16px;
  transform: rotate(-90deg);
  left: 6px;
  bottom: -8px;
  transition: all 300ms ease-in-out;
}