:root {
    --bg: rgba(0,0,0,0.7);
    --panel-bg: #fff;
    --btn-size: 35px;
  }

  .viewer-overlay {
    position: fixed;
    inset: 0;
    display: none;
    align-items: center;
    justify-content: center;
    background: var(--bg);
    z-index: 1000;
    padding: 20px;
    box-sizing: border-box;
  }

  .viewer-panel {
    position: relative;
    width: min(1200px, 96%);
    height: min(800px, 95%);
    padding-bottom: 30px;
    padding-top: 30px;
    background: var(--panel-bg);
    box-shadow: 0 12px 40px rgba(0,0,0,0.5);
    border-radius: 8px;
    overflow: hidden;
    display: flex;
    align-items: center;
    justify-content: center;
    box-sizing: border-box;
  }

  .page-container {
    width: 100%;
    height: 100%;
    padding: 32px;
    box-sizing: border-box;
    display: flex;
    align-items: center;
    justify-content: center;
  }

  /* 見開き用スタイル */
  .spread-wrapper {
    display: flex;
    width: 100%;
    height: 100%;
    align-items: center;
    justify-content: center;
  }

  /* 右開き（RTL）の見開き順序 */
  .spread-wrapper.rtl {
    flex-direction: row-reverse;
  }
  
  /* 左開き（LTR）の見開き順序 */
  .spread-wrapper.ltr {
    flex-direction: row;
  }

  .page-slot {
    flex: 1;
    height: 100%;
    display: flex;
    align-items: center;
    justify-content: center;
  }

  .page-slot img {
    max-width: 100%;
    max-height: 100%;
    object-fit: contain;
  }

  .nav-btn {
    position: absolute;
    top: 95%;
    transform: translateY(-50%);
    width: var(--btn-size);
    height: var(--btn-size);
    border-radius: 999px;
    background: rgba(255,255,255,0.9);
    border: none;
    box-shadow: 1px 3px 9px rgba(0,0,0,0.4);
    display: grid;
    place-items: center;
    cursor: pointer;
    padding: 10px;
    font-size: 15px;
    color: #FFFFFF;
    user-select: none;
    z-index: 10;
  }

  /* 矢印アイコンの設定 */
  .nav-left { 
    left: 15px; 
    content: url("/books/images/icon_arrow_prev.svg"); 
  }
  .nav-right { 
    right: 15px; 
    content: url("/books/images/icon_arrow_next.svg"); 
  }

  .close-btn {
    position: absolute;
    right: 10px;
    top: 10px;
    width: 40px;
    height: 40px;
    border-radius: 8px;
    background: white;
    border: none;
    font-size: 20px;
    cursor: pointer;
    z-index: 10;
  }

  .page-indicator {
    position: absolute;
    bottom: 10px;
    left: 50%;
    transform: translateX(-50%);
    background: rgba(255,255,255,0.9);
    padding: 6px 10px;
    border-radius: 999px;
    font-size: 14px;
  }

  .book-meta {
    position: absolute;
    top: 10px;
    left: 12px;
    background: rgba(255,255,255,0.9);
    padding: 6px 10px;
    border-radius: 6px;
    font-size: 14px;
  }