Pure CSS checkbox styling.

checkbox.scss

// Custom checkbox styling.
.checkbox-wrapper {
  $checkbox-height: 16px;
  $checkbox-width: 16px;

  label {
    display: inline-block;
    padding-left: ($checkbox-width + 15px);
    position: relative;

    &:after,
    &:before {
      content: '';
      display: inline-block;
      position: absolute;
    }

    // Before element is representing the checkbox's square.
    &:before {
      background-color: #fff;
      border: solid 1px #979797;
      border-radius: 2px;
      box-shadow: inset 0 1px 3px 0 rgba(0, 0, 0, 0.5);
      height: $checkbox-height;
      left: 0;
      top: 5px;
      width: $checkbox-width;
    }

    // After element is representing the checkbox's check mark.
    &:after {
      border-left: 3px solid $aqua;
      border-bottom: 3px solid $aqua;
      height: 8px;
      left: 4px;
      top: 4px;
      transform: rotate(-45deg);
      width: 15px;
    }
  }

  // Check/un-check interactions.
  .checkbox-element {
    opacity: 0;

    & + label::after {
      content: none;
    }

    &:checked + label::after {
      content: '';
    }
  }
}