My Custom Checkbox

_checkbox.scss

.my-checkbox {
  align-items: center;
  cursor: pointer;
  display: inline-flex;
}

.my-checkbox__input {
  // a11y-css-resetから引用
  // https://github.com/mike-engel/a11y-css-reset
  border: 0;
  clip: rect(0 0 0 0);
  clip-path: inset(50%);
  height: 1px;
  margin: -1px;
  overflow: hidden;
  padding: 0;
  position: absolute;
  white-space: nowrap;
  width: 1px;
}

.my-checkbox__icon {
  display: inline-block;
  height: 1.5em;
  position: relative;
  width: 1.5em;

  &::before,
  &::after {
    content: '';
    position: absolute;
  }

  &::before {
    border: 2px solid #999;
    height: 100%;
    left: 0;
    top: 0;
    transition: border-color .5s, opacity .5s, transform .5s $easeOutCirc;
    width: 100%;

    // input[type=checkbox]がチェックされたとき
    .my-checkbox__input:checked + & {
      border-color: #779a75;
      opacity: 0;
      transform: rotate(45deg) scale3d(2, 2, 1);
      pointer-events: none; // クリッカブルな箇所が広がってしまうのでクリックを無効にする
    }
  }

  &::after {
    border-bottom: 2px solid transparent;
    border-left: 2px solid transparent;
    height: .5em;
    left: .25em;
    opacity: 0;
    top: .375em;
    transform: rotate(-225deg);
    transition: opacity .5s, transform .5s $easeOutCirc;
    width: 1em;

    // input[type=checkbox]がチェックされたとき
    .my-checkbox__input:checked + & {
      border-bottom: 2px solid #779a75;
      border-left: 2px solid #779a75;
      opacity: 1;
      transform: rotate(-45deg);
    }
  }
}

.my-checkbox__text {
  display: inline-block;
  letter-spacing: .01em;
  line-height: 1.5;
  position: relative;
  transition: color .3s;
  
  @mixin isActive {
    color: #779a75;
  }
  
  .my-checkbox__input:checked ~ & {
    @include isActive;
  }
  
  // :focus-visibleで指定することでTab移動でfocusされた場合のみfocusを可視化する
  .my-checkbox__input.focus-visible ~ & {
    @include isActive;
  }
    
  @media(hover) {
    &:hover {
      @include isActive;
    }
  }

  &::after {
    background-color: #999;
    bottom: -2px;
    content: '';
    display: inline-block;
    height: 2px;
    left: 0;
    position: absolute;
    transform: scale3d(0, 1, 1);
    transform-origin: right;
    transition: transform .3s;
    width: 100%;
    
    @mixin isActive {
      transform: scale3d(1, 1, 1);
      transform-origin: left;
    }

    // :focus-visibleで指定することでTab移動でfocusされた場合のみfocusを可視化する
    .my-checkbox__input:focus-visible ~ & {
      @include isActive;
    }
    
    @media(hover) {
      .my-checkbox:hover & {
        @include isActive;
      }
    }
  }

  .my-checkbox__icon + & {
    margin-left: 1em;
  }
}

checkbox.html

<label class="my-checkbox">
  <input class="my-checkbox__input" type="checkbox">
  <span class="my-checkbox__icon"></span>
  <span class="my-checkbox__text">ラベル</span>
</label>