【クリエイターモード】テンプレートBasicsで、PC表示の商品詳細ページのヘッダーをスマホ用ヘッダーに変えたいです。方法を教えてください。

/* PC商品詳細ページ スマホ用ヘッダー表示 */
@media (min-width: 769px) {
  span.cart-badge {
    top: -10px;
    right: -14px;
  }
  .header{
    width: 100%;
  }
  .header-wrap {
    justify-content: center;
  }
  .shop-logo {
    margin: 0;
  }
  .header-sns {
    display: none;
  }
  .sns-link-list-sp {
    display: flex;
    padding-top: 20px;
  }
  .sns-link-list-sp .sns-link {
    padding: 0 0 0 14px;
  }
  .nav, .second-nav {
    display: none;
  }
  .side-bar {
    display: none;
  }
  .banner-area li {
    flex: 0 0 49%;
    max-width: 49%;
    margin-bottom: 1.6%;
  }
  .header-info {
    flex-direction: column;
    text-align: center !important;
  }
  .header-info dt, .header-info dd {
    text-align: center !important;
  }
  .shop-logo span {
    display: none;
  }
  #start-contents .contents-section {
    margin: 0 auto;
  }
  /*------------------
    hamburger
    ------------------*/
  .wrapper {
    height: 100%;
    overflow-x: hidden;
    position: relative;
    display: block;
  }
  .sp-nav-wrap {
    display: block;
  }
  .sp-nav-wrap a {
    font-weight: 700;
  }
  .overlay {
    content: "";
    display: block;
    width: 0;
    height: 0;
    background-color: rgba(0, 0, 0, 0.5) !important;
    position: absolute;
    top: 0;
    left: 0;
    z-index: 2;
    opacity: 0;
    transition: opacity .5s;
  }
  .overlay.open {
    width: 100%;
    height: 100%;
    opacity: 1;
  }
  .menu-trigger {
    display: inline-block;
    width: 28px;
    height: 28px;
    vertical-align: middle;
    cursor: pointer;
    position: fixed;
    top: 8px!important;
    left: 16px;
    z-index: 100;
  }
  .menu-trigger span {
    display: inline-block;
    box-sizing: border-box;
    position: absolute;
    left: 0;
    width: 80%;
    height: 4px;
    background-color: #000;
    transition: all .5s;
  }
  .menu-trigger.active span {
    background-color: #000;
  }
  .menu-trigger span:nth-of-type(1) {
    top: 4px;
  }
  .menu-trigger.active span:nth-of-type(1) {
    transform: translateY(12px) rotate(-45deg);
  }
  .menu-trigger span:nth-of-type(2) {
    top: 12px;
  }
  .menu-trigger.active span:nth-of-type(2) {
    opacity: 0;
  }
  .menu-trigger span:nth-of-type(3) {
    bottom: 4px;
  }
  .menu-trigger.active span:nth-of-type(3) {
    transform: translateY(-4px) rotate(45deg);
  }
  nav {
    width: 250px;
    height: 100%;
    padding-top: 100px;
    background: #fff !important;
    position: fixed;
    top: 0;
    left: 0;
    z-index: 10;
    transform: translate(-250px);
    transition: all .5s;
  }
  nav.open {
    transform: translate(0, 0);
    overflow: scroll;
    overflow-x: hidden;
    width: 100%;
    height: 100%;
  }
  nav li {
    color: #000;
    text-align: left;
    padding: 10px 20px;
  }
  nav li a {
    color: #000;
  }
  .accordion-container {
    position: relative;
    width: 100%;
    cursor: pointer
  }
  .accordion-container .article-title {
    display: block;
    position: relative;
    margin: 0;
    font-weight: 700;
    color: #000;
    cursor: pointer;
  }
  .accordion-container .article-title:hover i:before,
  .accordion-container .article-title:hover i:active,
  .accordion-container .content-entry.open i {
    color: white;
  }
  .article-title {
    position: relative;
  }
  .article-title:after {
    content: "";
    position: absolute;
    right: 16px;
    top: 10%;
    transition: all 0.2s ease-in-out;
    display: block;
    width: 8px;
    height: 8px;
    border-top: solid 2px #6E6E6E;
    border-right: solid 2px #6E6E6E;
    -webkit-transform: rotate(135deg);
    transform: rotate(135deg);
  }
  .article-title.open:after {
    -webkit-transform: rotate(-45deg);
    transform: rotate(-45deg);
    top: 45%;
  }
  .accordion-content {
    display: none;
    padding: 24px 6px 0;
    font-family: 'Noto Sans JP', sans-serif;
  }
  .accordion-content p {
    position: relative;
    padding-bottom: 20px;
    margin-bottom: 20px;
    display: block;
  }
  .accordion-content a {
    position: absolute;
    display: inline-block;
    width: 100%;
    height: 100%;
    top: 0;
    left: 0;
    color: #000;
  }
  .accordion-container {
    margin: 0;
  }
  dl.search1 {
    position: relative;
    background-color: #fff;
    border-bottom: 1px solid #aaa;
  }
  dl.search1 dt {
    padding: 12px 0px;
  }
  dl.search1 dt input {
    border: none;
    border-radius: 0;
    outline: none;
    background: none;
  }
  dl.search1 dd {
    position: absolute;
    top: 0;
    right: 0;
  }
  dl.search1 dd button {
    display: block;
    padding: 10px;
    background: none;
    border: none;
  }
  dl.search1 dd button span {
    display: block;
    width: 20px;
    height: 20px;
    background: url('/view/images/template/6/search_icon.png') no-repeat scroll 0 0;
  }
  .search-link-sp {
    margin-bottom: 16px;
  }
  .sp-second-nav-wrap {
    display: flex;
    position: absolute;
    top: 13px;
    right: 16px;
  }
  .cart-link {
    margin-left: 16px;
  }
  .information-label {
    margin: 0 0 8px 0;
  }
  /*------------------
    detail
    ------------------*/
  .item-inner {
    margin-top: 100px;
  }
  .header-info {
    flex-direction: unset;
  }
  .header-wrap {
    padding: 3px;
  }
  .header-info {
    padding: 5px;
  }
  .header-info dd {
    margin-left: 5px;
  }
  .header-inner:first-child {
    border:none;
  }
}

補足

商品詳細ページの「CSS」欄に記述した内容は、商品詳細ページのみに適用されます。
トップページやカテゴリーページのヘッダーには影響しません。
なお、上記のCSSは商品詳細ページ用のCSSのため、他のページの「CSS」欄に記述した場合は崩れが発生します。