edx-platform/lms/static/sass/course/_textbook.scss

div.book-wrapper {
  max-width: map-get($container-max-widths, xl);
  margin: 0 auto;
  width: 100%;

  #open_close_accordion {
    display: none;
  }

  .pdfbook-wrap {
    display: table;
    width: 100%;
  }

  .pdfbook-wrap-inner {
    display: table-row;
  }

  section.book-sidebar {
    @extend .sidebar;
    @extend .tran;

    box-sizing: border-box;
    padding: ($baseline/2) 0;
    border-radius: 3px 0 0 3px;
    border: 1px solid $gray-l3;
    border-right: none;
    width: 180px;

    #booknav {
      list-style: none;

      .chapter {
        line-height: 1.4em;
      }

      .page-number {
        @include float(right);

        width: 12%;
        font-size: 0.8em;
        line-height: 2.1em;
        text-align: right;
        color: #9a9a9a;
        opacity: 0;

        @include transition(opacity 0.15s linear 0s);
      }

      li {
        background: none;
        border-bottom: 0;
        padding-left: ($baseline/2);

        a {
          @include clearfix();

          padding: 0;
          color: theme-color("primary");

          &:hover,
          &:focus {
            background-color: transparent;
            color: $uxpl-blue-hover-active;

            .page-number {
              opacity: 1;
            }
          }
        }

        div.hitarea {
          background-image: url('#{$static-path}/images/treeview-default.gif');
          position: relative;
          top: 4px;

          &:hover,
          &:focus {
            filter: alpha(opacity=60);
            opacity: 0.6;
          }
        }

        ul {
          background: none;
          margin-top: lh(0.25);
          padding-top: lh(0.25);

          li {
            padding-bottom: ($baseline/2);
          }
        }
      }

      > li {
        padding: ($baseline/4) 6px;
        margin: ($baseline/4) ($baseline/2);
      }
    }
  }

  .book {
    @extend .content;

    padding: 0;
    width: 76%;

    nav {
      @extend .clearfix;

      a {
        @extend .block-link;

        padding: 0 lh();
      }

      ul {
        @extend .clearfix;

        li {
          position: absolute;
          height: 100%;
          width: flex-grid(2, 8);
          z-index: 1;

          a {
            background-color: rgba(#000, 0.7);
            background-position: center;
            background-repeat: no-repeat;
            box-sizing: border-box;
            display: table;
            height: 100%;
            opacity: 0;
            filter: alpha(opacity=0);
            text-indent: -9999px;

            @include transition(none);

            vertical-align: middle;
            width: 100%;

            &:hover,
            &:focus {
              opacity: 1;
            }

            &.is-disabled {
              display: none;
            }
          }

          &.last {
            left: 0;

            a {
              background-image: url('#{$static-path}/images/textbook/textbook-left.png');
            }
          }

          &.next {
            right: 0;

            a {
              background-image: url('#{$static-path}/images/textbook/textbook-right.png');
            }
          }
        }
      }

      &.bottom-nav {
        border-bottom: 0;
        margin-bottom: -(lh());
        margin-top: lh();
      }
    }

    section.page {
      border-left: 1px solid $border-color;
      background-color: $white;
      position: relative;
      text-align: center;
      border-radius: 0 3px 3px 0;

      img {
        max-width: 100%;
      }

      #viewer {
        padding: $baseline;
      }

      div {
        text-align: left;
        line-height: 1.6em;
        margin: ($baseline/4);

        .Paragraph,
        h2 {
          margin-top: ($baseline/2);
        }
      }
    }
  }

  &.closed {
    section.book-sidebar {
      width: flex-grid(0.6);

      header#open_close_accordion {
        padding: 0;

        a {
          background-image: url('#{$static-path}/images/slide-right-icon.png');
        }

        h2 {
          padding: 0;
          visibility: hidden;
          width: 10px;
        }
      }

      ul#booknav {
        max-height: 100px;
        overflow: hidden;
        padding: 0;
        visibility: hidden;
        width: 10px;
      }
    }

    section.course-content {
      width: flex-grid(11.5) + flex-gutter();
    }
  }
}