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

.container {
  width: 100vw;
  height: 100vh;
  
  display: flex;
  justify-content: center;
  align-items: center;
  
  background-color: #121420;
  color: white;
}


.toggle {
  --toggle-width: 8em;
  --toogle-height: 4em;
  --toggle-color: #f7ce5b;
  --toggle-padding-horizontal: calc((var(--toogle-height) - var(--knob-size)) / 2);
  
  --knob-size: 3em;
  --knob-color: #9f2042;
  
  display: flex;
  align-items: center;
  justify-content: flex-start;
  
  width:  var(--toggle-width);
  height: var(--toogle-height);
  border-radius: 100em;
  margin-left: 0;
  padding: 0 var(--toggle-padding-horizontal);
  
  background-color: var(--toggle-color);
}

.toggle::after {
  content: "";
  display: block;
  
  width:  var(--knob-size);
  height: var(--knob-size);
  border-radius: 100em;
  
  background-color: var(--knob-color);
  transition: margin-left 300ms ease;
}


.toggle--sliding::after {
  margin-left: calc(var(--toggle-width) - var(--toggle-padding-horizontal)*2 - var(--knob-size));
}

var toggle = document.querySelector("#toggle");

toggle.addEventListener("click", () => {
  toggle.classList.toggle("toggle--sliding");
});