* {
      margin: 0;
      padding: 0;
    }

    #book {
      width: 600px;
      min-height: 800px;
      background-color: #eee;
      background-image: linear-gradient(to bottom right, #003, #005);
      color: #444;
      display: block;
      margin: 0 auto;
      padding-top: 2rem;
      cursor: default;
      transform-style: preserve-3d;
      transform-origin: left center;
      box-shadow: 0 4px 8px rgba(0, 0, 0, 0.2);
    }

    #book_face {
      width: fit-content;
      margin: 0 auto;
      color: white;
    }

    #book_index {
      width: 500px;
      margin: 0 auto;
      display: none;
    }

    .book_name_item {
      margin-bottom: 2rem;
    }

    .book_name_item span {
      font-size: 1rem;
      font-weight: bolder;
    }

    .book_name_item p {
      display: inline;
      cursor: pointer;
      font-weight: normal;
    }

    .book_name_item p:hover {
      font-weight: bold;
    }

    #nameCate span {
      font-weight: normal;
    }

    #nameCate span:hover {
      font-weight: bold;
    }

    .face_button {
      display: block;
      border: none;
      width: fit-content;
      margin: 0 auto;
      text-align: center;
	    font-size: .75rem;
      cursor: pointer;
    }

    .face_button div {
      font-size: 3rem;
    }

    #beian {
      margin: 1rem auto;
      text-align: center;
      font-size: .75rem;
      color: #666;
    }

    #beian a {
      text-decoration: none;
      color: #666;
    }

    #book_content {
      margin-left: 600px;
      padding: 0rem 4rem 50rem 4rem;
      display: none;
    }

    #book_content p {
      text-indent: 2rem;
      line-height: 2rem;
      letter-spacing: 1px;
    }

    #book_content h2 {
      margin-top: 2rem;
      padding: 0 0 2px 5px;
      background-color: red;
      color: white;
      letter-spacing: 3px;
    }

    #book_content h3 {
      margin-top: 1rem;
      color: red;
      font-size: 1.5rem;
      letter-spacing: 2px;
    }

    #book_content h4 {
      margin-top: .5rem;
      font-size: 1.2rem;
      letter-spacing: 2px;
    }

    #book_content h5 {
      margin: .5rem auto;
      letter-spacing: 1px;
      color: blue;
    }

    #book_content .concept {
      font-weight: bolder;
      color: blue;
    }

    #book_content img {
      width: 100%;
      margin: 0 auto;
      display: block;
    }

    #book_content img.winshot {
      width: 97%;
      margin: 1rem;
      box-shadow: 0 8px 16px rgba(0, 0, 0, 0.2);
    }

    #outlines {
      font-size: 1rem;
    }

    #outlines ul {
      list-style-type: none;
      padding-left: 24px;
      margin: 0;
    }

    #outlines li {
      margin: 5px 0;
      cursor: pointer;
      white-space: nowrap;
      overflow: hidden;
      text-overflow: ellipsis;
    }

    #outlines li.active {
      font-weight: bold;
    }

    #outlines .collapsible {
      position: relative;
    }

    #outlines .collapsible-content {
      display: block;
    }

    #outlines .collapsible-content.collapsed {
      display: none;
    }

    #mobile_bar {
      display: none;
    }

    #menu_mask {
      display: none;
    }

    @media only screen and (max-width: 768px) {

      #book {
        width: 100%;
        min-height: 640px;
      }

      #book_content {
        margin-left: 0;
        margin-top: 5rem;
        padding: 0rem 1rem 30rem 1rem;
      }

      #mobile_bar {
        position: fixed;
        top: 0;
        left: 0;
        right: 0;
        padding: 16px;
        background-color: #eee;
        display: flex;
        justify-content: space-between;
        list-style: none;
      }

      #mobile_bar li {
        font-size: 1.75rem;
      }

      #menu_mask {
        position: fixed;
        top: 0;
        bottom: 0;
        left: 0;
        right: 0;
        background-color: #00000080;
        z-index: 999;
      }

      #outlines {
        position: fixed;
        top: 0;
        left: 0;
        width: 75%;
        background-color: white;
      }

      #book_content img.winshot {
        margin: 0;
      }

    }