An iOS-style toggle switch.

switch.scss

/* 
    <label className="switch">
        <input type="checkbox" />
        <div className="checkbox"></div>
    </label>
*/

.switch {
  $active-color: #27c940;
  $switch-height: 24px;
  $switch-padding: 2px;
  $switch-width: $switch-height * 1.625;
  $switch-radius: $switch-height;
  $knob-size: $switch-height - ($switch-padding * 2);
  $knob-radius: $switch-height - ($switch-padding * 2);
  $switch-bg: white;
  $transition-duration: 0.3s;

  cursor: pointer;
  display: inline-block;

  .checkbox {
    background-color: darken($switch-bg, 9%);
    border-radius: $switch-radius;
    border: none;
    height: $switch-height;
    position: relative;
    transition: background-color $transition-duration;
    width: $switch-width;
    z-index: 0;

    &::before {
      background-color: $switch-bg;
      border-radius: $switch-radius;
      bottom: 0;
      content: "";
      height: $knob-radius;
      left: 2px;
      position: absolute;
      right: 0;
      top: 2px;
      transform: scale(1);
      transition: all $transition-duration;
      width: $switch-width - ($switch-padding * 2);
      z-index: 1;
    }

    &::after {
      background-color: $switch-bg;
      border-radius: $knob-radius;
      bottom: 0;
      box-shadow: 0 1px 2px transparentize(black, 0.6);
      content: "";
      height: $knob-size;
      left: 2px;
      position: absolute;
      right: 0;
      top: 2px;
      transition: all $transition-duration;
      width: $knob-size;
      z-index: 2;
    }
  }

  input[type="checkbox"] {
    display: none;

    &:checked + .checkbox {
      background-color: $active-color;

      &::before {
        transform: scale(0);
      }

      &::after {
        left: $switch-width - $knob-size - $switch-padding;
      }
    }
  }
}