【jQuery】チェックボックスにチェックを入れるとボタンが活性化する

<section>

  <div class="notes_required">
    <div class="checkBtn_area">
      <label for="checkBtn" class="checkBtn"><input id="checkBtn" type="checkbox"><span class="label_inner">同意する</span></label>
    </div>
    <p class="check_text_b">チェックを入れると「ボタン」が有効となります。</p>
  </div>

  <div class="btnArea">
    <input type="submit" value="">
    <a href="https://125naroom.com/web/3191" target="_blank" class="btn_one _a">ボタン</a>
  </div>

  <div class="btnArea">
    <input type="submit" value="">
    <a href="https://125naroom.com/web/3191" target="_blank" class="btn_one _b">ボタン</a>
  </div>

</section>

/*------------------------------------------------------------
.notes_required
------------------------------------------------------------*/

.notes_required {
  text-align: center;
  background: #fff;
  border: 2px solid #e8dc6a;
  padding: 30px 20px;
}
.notes_required .check_text_b {
  font-size: 16px;
  margin: 0;
}
.notes_required .checkBtn_area {
  max-width: 400px;
  margin: 15px auto 10px;
  border-radius: 12px;
  background: #f3efe6;
  padding: 20px 0;
  transition: .2s;
}
.notes_required._check .checkBtn_area {
  background: #e8dc6a;
}
.notes_required label {
  color: #2b2a27;
  font-size: 20px;
  border-bottom: 1px solid rgba(255, 255, 255, 0);
  cursor: pointer;
  transition: .3s;
  position: relative;
}
.notes_required label .label_inner {
  padding-left: 22px;
}
.notes_required label .label_inner:before {
  content: "";
  width: 24px;
  height: 24px;
  background: #fff;
  border: 4px solid #2b2a27;
  box-sizing: border-box;
  position: absolute;
  top: 50%;
  left: 0;
  margin-top: -13px;
}
.notes_required._check label .label_inner:after {
  content: '';
  width: 20px;
  height: 12px;
  border-top: 6px solid #2b2a27;
  border-right: 6px solid #2b2a27;
  transform: rotate(130deg);
  position: absolute;
  top: 50%;
  left: 0;
  margin-top: -.9em;
}
.notes_required label input {
  position: relative;
  z-index: -1;
}
@media screen and (min-width: 768px) {
  .notes_required label:hover {
    border-bottom: 2px solid #2b2a27;
  }
}
@media screen and (max-width: 1024px) {
  .notes_required label {
    font-size: 18px;
  }
  .notes_required .check_text_b {
    font-size: 14px;
  }
  .notes_required label .label_inner {
    padding-left: 10px;
  }
  .notes_required label .label_inner:before {
    width: 20px;
    height: 20px;
    margin-top: -10px;
  }
  .notes_required._check label .label_inner:after {
    width: 16px;
    height: 8px;
    margin-top: -0.8em;
  }
}
@media screen and (max-width: 767px) {
  .notes_required {
    padding: 20px 15px;
  }
  .notes_required .check_text_b {
    font-size: 13px;
  }
}

/*------------------------------------------------------------
.btnArea
------------------------------------------------------------*/

.btnArea {
  max-width: 400px;
  margin: 30px auto 0;
  position: relative;
}
/* 押せないあいだは、透明の input をボタンの上にかぶせる */
.btnArea input[type="submit"] {
  position: absolute;
  top: 0;
  left: 0;
  right: 0;
  margin: 0 auto;
  width: 100%;
  height: 100%;
  border: none;
  border-radius: 0;
  background: rgba(255, 255, 255, 0);
  padding: 0;
  cursor: default;
  z-index: 1;
  outline: none;
  transition: .3s;
  box-sizing: border-box;
  appearance: none;
}
.btnArea._check input[type="submit"] {
  z-index: -1;
}
a.btn_one {
  display: flex;
  justify-content: center;
  align-items: center;
  background: #e8e3d8;
  border: 2px solid #e8e3d8;
  border-radius: 12px;
  box-sizing: border-box;
  box-shadow: 0px 0px 0px 0px #6b675f;
  width: 100%;
  height: 80px;
  padding: 0 10% 0 6%;
  color: #6b675f;
  font-size: 24px;
  font-weight: bold;
  text-align: left;
  text-decoration: none;
  position: relative;
  transition: .2s;
}
a.btn_one:before {
  content: "";
  display: inline-block;
  width: 0;
  height: 0;
  border-style: solid;
  border-width: 10px 0 10px 12px;
  border-color: transparent transparent transparent currentColor;
  position: absolute;
  top: 50%;
  right: 8%;
  margin-top: -11px;
}
._check a.btn_one._a {
  background: #2b2a27;
  border-color: #2b2a27;
  color: #fff;
  box-shadow: 0px 5px 0px 0px #6b675f;
}
._check a.btn_one._a:hover {
  background: #fff;
  color: #2b2a27;
}
._check a.btn_one._b {
  background: #e8dc6a;
  border-color: #e8dc6a;
  color: #2b2a27;
  box-shadow: 0px 5px 0px 0px #2b2a27;
}
._check a.btn_one._b:hover {
  background: #2b2a27;
  border-color: #2b2a27;
  color: #fff;
}
@media screen and (max-width: 1024px) {
  a.btn_one {
    height: 60px;
    font-size: 20px;
  }
}
@media screen and (max-width: 767px) {
  a.btn_one {
    font-size: 16px;
  }
}

/* 動きを減らす設定のとき */
@media (prefers-reduced-motion: reduce) {
  .notes_required .checkBtn_area,
  .notes_required label,
  a.btn_one { transition: none; }
}

//チェックが入ったら、ボタンを押せる
$(function () {
  $('#checkBtn').on('change', function () {
    $('.notes_required, .btnArea').toggleClass('_check', this.checked);
  });
});