tsmd/_checkbox.scss

## _checkbox.scss
@charset "UTF-8";

.Checkbox {
  @at-root {
    @function checked-icon($color: #fff) {
      $color: '' + $color;
      $color: '%23' + str-slice($color, 2);
      @return 'data:image/svg+xml,%3Csvg%20xmlns%3D%22http%3A%2F%2Fwww.w3.org%2F2000%2Fsvg%22%20viewBox%3D%220%200%2024%2024%22%3E%3Cpath%20d%3D%22M9%2016.17L4.83%2012l-1.42%201.41L9%2019%2021%207l-1.41-1.41z%22%20fill%3D%22#{$color}%22%2F%3E%3C%2Fsvg%3E';
    }

    & {
      position: relative;
      z-index: 0;
      display: inline-flex;
      justify-content: flex-start;
      align-items: baseline;
      line-height: 1.8;
    }

    .Checkbox__input {
      position: absolute;
      z-index: -1;
      opacity: 0;
    }

    .Checkbox__icon {
      flex: 0 0 auto;
      position: relative;
      top: 0.1em; // vertical-align としての役割
      width: 1em;
      height: 1em;
      border-radius: 4px;
      background-color: $color-gray30;

      // クリック範囲拡張
      &::before {
        content: '';
        position: absolute;
        top: -50%;
        left: -50%;
        width: 200%;
        height: 200%;
      }

      &::after {
        content: '';
        position: absolute;
        top: 0;
        right: 0;
        bottom: 0;
        left: 0;
        display: none;
        width: (12px / 16px) * 100%;
        height: (12px / 16px) * 100%;
        margin: auto;
        background: url(checked-icon(#fff)) no-repeat center;
      }
    }

    .Checkbox__label {
      margin-left: (6px / 16px) * 1em;
    }

    // フォーカス
    :focus.focus-visible ~ .Checkbox__icon {
      box-shadow: 0 0 0 4px rgba($color-primary, 0.5);
    }

    // チェック済み
    :checked ~ .Checkbox__icon {
      background-color: $color-primary;

      &::after {
        display: block;
      }
    }

    // 中間状態
    :indeterminate ~ .Checkbox__icon {
      background-color: $color-primary-light;

      &::after {
        display: block;
        width: (6px / 16px) * 100%;
        height: (2px / 16px) * 100%;
        background: #fff;
      }
    }

    // 使用不可
    :disabled {
      & ~ .Checkbox__icon {
        background-color: $color-gray10;

        &::after {
          background-image: url(checked-icon(#8ca0a5));
        }
      }

      & ~ .Checkbox__label {
        color: $color-gray60;
      }
    }
  }
}

## checkbox.html
<!DOCTYPE html>
<html lang="ja">
<title>Checkbox</title>

<label class="Checkbox">
  <input class="Checkbox__input" type="checkbox" aria-label="テキストラベル">
  <span class="Checkbox__icon"></span>
</label>

<label class="Checkbox">
  <input class="Checkbox__input" type="checkbox">
  <span class="Checkbox__icon"></span>
  <span class="Checkbox__label">
    テキストラベル
  </span>
</label>
	@charset "UTF-8";

	.Checkbox {
	@at-root {
	@function checked-icon($color: #fff) {
	$color: '' + $color;
	$color: '%23' + str-slice($color, 2);
	@return 'data:image/svg+xml,%3Csvg%20xmlns%3D%22http%3A%2F%2Fwww.w3.org%2F2000%2Fsvg%22%20viewBox%3D%220%200%2024%2024%22%3E%3Cpath%20d%3D%22M9%2016.17L4.83%2012l-1.42%201.41L9%2019%2021%207l-1.41-1.41z%22%20fill%3D%22#{$color}%22%2F%3E%3C%2Fsvg%3E';
	}

	& {
	position: relative;
	z-index: 0;
	display: inline-flex;
	justify-content: flex-start;
	align-items: baseline;
	line-height: 1.8;
	}

	.Checkbox__input {
	position: absolute;
	z-index: -1;
	opacity: 0;
	}

	.Checkbox__icon {
	flex: 0 0 auto;
	position: relative;
	top: 0.1em; // vertical-align としての役割
	width: 1em;
	height: 1em;
	border-radius: 4px;
	background-color: $color-gray30;

	// クリック範囲拡張
	&::before {
	content: '';
	position: absolute;
	top: -50%;
	left: -50%;
	width: 200%;
	height: 200%;
	}

	&::after {
	content: '';
	position: absolute;
	top: 0;
	right: 0;
	bottom: 0;
	left: 0;
	display: none;
	width: (12px / 16px) * 100%;
	height: (12px / 16px) * 100%;
	margin: auto;
	background: url(checked-icon(#fff)) no-repeat center;
	}
	}

	.Checkbox__label {
	margin-left: (6px / 16px) * 1em;
	}

	// フォーカス
	:focus.focus-visible ~ .Checkbox__icon {
	box-shadow: 0 0 0 4px rgba($color-primary, 0.5);
	}

	// チェック済み
	:checked ~ .Checkbox__icon {
	background-color: $color-primary;

	&::after {
	display: block;
	}
	}

	// 中間状態
	:indeterminate ~ .Checkbox__icon {
	background-color: $color-primary-light;

	&::after {
	display: block;
	width: (6px / 16px) * 100%;
	height: (2px / 16px) * 100%;
	background: #fff;
	}
	}

	// 使用不可
	:disabled {
	& ~ .Checkbox__icon {
	background-color: $color-gray10;

	&::after {
	background-image: url(checked-icon(#8ca0a5));
	}
	}

	& ~ .Checkbox__label {
	color: $color-gray60;
	}
	}
	}
	}
	<!DOCTYPE html>
	<html lang="ja">
	<title>Checkbox</title>

	<label class="Checkbox">
	<input class="Checkbox__input" type="checkbox" aria-label="テキストラベル">
	<span class="Checkbox__icon"></span>
	</label>

	<label class="Checkbox">
	<input class="Checkbox__input" type="checkbox">
	<span class="Checkbox__icon"></span>
	<span class="Checkbox__label">
	テキストラベル
	</span>
	</label>