:root {
  --bg-gradient: linear-gradient(135deg, #0f172a 0%, #1e1b4b 50%, #0f172a 100%);
  --panel-bg: rgba(30, 41, 59, 0.85);
  --panel-border: rgba(255, 255, 255, 0.12);
  --primary: #6366f1;
  --primary-hover: #4f46e5;
  --text-main: #f8fafc;
  --text-muted: #94a3b8;
}

* { box-sizing: border-box; margin: 0; padding: 0; user-select: none; }

body {
  font-family: 'Inter', sans-serif;
  background: var(--bg-gradient);
  height: 100vh;
  color: var(--text-main);
  display: flex;
  flex-direction: column;
  overflow: hidden;
}

/* Header & Navigation */
header {
  display: flex;
  justify-content: space-between;
  align-items: center;
  padding: 0.75rem 1.5rem;
  background: rgba(15, 23, 42, 0.75);
  backdrop-filter: blur(12px);
  border-bottom: 1px solid var(--panel-border);
  z-index: 20;
  flex-shrink: 0;
}

.logo {
  display: flex;
  align-items: center;
  gap: 0.75rem;
  font-weight: 700;
  font-size: 1.2rem;
  color: #fff;
}
.logo i { color: var(--primary); }

/* Floating Controls Toolbar */
.controls {
  display: flex;
  align-items: center;
  gap: 0.4rem;
  background: var(--panel-bg);
  backdrop-filter: blur(16px);
  padding: 0.4rem 0.8rem;
  border-radius: 9999px;
  border: 1px solid var(--panel-border);
  box-shadow: 0 10px 25px -5px rgba(0, 0, 0, 0.5);
}

.btn {
  background: transparent;
  color: var(--text-main);
  border: none;
  padding: 0.45rem 0.75rem;
  border-radius: 9999px;
  cursor: pointer;
  font-weight: 500;
  font-size: 0.85rem;
  display: inline-flex;
  align-items: center;
  gap: 0.4rem;
  transition: all 0.2s ease;
}

.btn:hover:not(:disabled) {
  background: rgba(255, 255, 255, 0.12);
  color: #fff;
}
.btn-primary { background: var(--primary); color: #fff; }
.btn-primary:hover:not(:disabled) { background: var(--primary-hover); }
.btn:disabled { opacity: 0.3; cursor: not-allowed; }

.divider { width: 1px; height: 18px; background: var(--panel-border); margin: 0 2px; }
.info-text { font-size: 0.82rem; font-weight: 500; color: var(--text-muted); min-width: 45px; text-align: center; }

input[type="file"] { display: none; }

/* Main Container */
main {
  flex: 1;
  display: flex;
  justify-content: center;
  align-items: flex-start;
  padding: 1.5rem;
  position: relative;
  overflow: auto;
}

.upload-zone {
  margin: auto;
  border: 2px dashed rgba(255, 255, 255, 0.2);
  border-radius: 1.5rem;
  padding: 3rem 2rem;
  text-align: center;
  max-width: 500px;
  width: 100%;
  background: rgba(30, 41, 59, 0.4);
  backdrop-filter: blur(8px);
  cursor: pointer;
  transition: all 0.3s ease;
}
.upload-zone:hover { border-color: var(--primary); background: rgba(30, 41, 59, 0.7); }
.upload-icon { font-size: 3rem; color: var(--primary); margin-bottom: 1rem; }

.loading-box { margin: auto; display: none; flex-direction: column; align-items: center; gap: 1rem; }
.spinner {
  width: 44px; height: 44px;
  border: 4px solid rgba(255, 255, 255, 0.1);
  border-top-color: var(--primary);
  border-radius: 50%;
  animation: spin 1s linear infinite;
}
@keyframes spin { to { transform: rotate(360deg); } }

/* Flipbook Container */
.flipbook-stage {
  display: none;
  justify-content: center;
  align-items: center;
  transition: transform 0.2s cubic-bezier(0.25, 1, 0.5, 1);
  transform-origin: top center;
  margin-top: 0.5rem;
}
.flip-book { box-shadow: 0 25px 50px -12px rgba(0, 0, 0, 0.8); border-radius: 4px; }
.page { background-color: #f8fafc; overflow: hidden; }
.page canvas { width: 100%; height: 100%; object-fit: contain; }

/* Bảng thumbnails hình thu nhỏ */
.thumbs-panel {
  position: fixed;
  top: 60px; right: -320px;
  width: 300px; height: calc(100vh - 60px);
  background: rgba(15, 23, 42, 0.95);
  backdrop-filter: blur(16px);
  border-left: 1px solid var(--panel-border);
  z-index: 30;
  transition: right 0.3s ease;
  padding: 1rem;
  display: flex;
  flex-direction: column;
  gap: 1rem;
}
.thumbs-panel.active { right: 0; }
.thumbs-header { display: flex; justify-content: space-between; align-items: center; font-weight: 600; }
.thumbs-grid {
  flex: 1; overflow-y: auto; display: grid;
  grid-template-columns: repeat(2, 1fr); gap: 0.75rem;
}
.thumb-item {
  border: 2px solid transparent; border-radius: 6px; overflow: hidden;
  cursor: pointer; background: #334155; transition: all 0.2s ease; position: relative;
}
.thumb-item.active { border-color: var(--primary); }
.thumb-item img { width: 100%; display: block; }
.thumb-number {
  position: absolute; bottom: 4px; right: 4px;
  background: rgba(0,0,0,0.7); font-size: 0.7rem; padding: 2px 6px; border-radius: 4px;
}

.progress-bar-container { position: fixed; bottom: 0; left: 0; width: 100%; height: 4px; background: rgba(255, 255, 255, 0.05); z-index: 20; }
.progress-bar { height: 100%; width: 0%; background: var(--primary); transition: width 0.3s ease; }

.copyright-footer {
  position: fixed;
  bottom: 10px;
  right: 15px;
  font-size: 0.75rem;
  z-index: 25;
  background: rgba(15, 23, 42, 0.75);
  padding: 4px 12px;
  border-radius: 9999px;
  backdrop-filter: blur(8px);
  border: 1px solid var(--panel-border);
  box-shadow: 0 4px 12px rgba(0, 0, 0, 0.3);
  transition: all 0.2s ease;
}

.copyright-footer:hover {
  background: rgba(30, 41, 59, 0.95);
  border-color: var(--primary);
  transform: translateY(-1px);
}

.copyright-footer a {
  color: var(--text-muted);
  text-decoration: none;
  display: flex;
  align-items: center;
  gap: 0.4rem;
  transition: color 0.2s ease;
}

.copyright-footer a .home-icon {
  color: var(--primary);
  font-size: 0.8rem;
  transition: transform 0.2s ease;
}

.copyright-footer a:hover {
  color: #fff;
}

.copyright-footer a:hover .home-icon {
  transform: scale(1.15); /* Phóng to nhẹ icon khi di chuột */
  color: #fff;
}

.copyright-footer strong {
  color: var(--primary);
}

.copyright-footer a:hover strong {
  color: #fff;
}

.logo {
  display: flex;
  align-items: center;
  gap: 0.75rem;
  font-weight: 700;
  font-size: 1.25rem;
  color: #fff;
}

/* CSS MỚI CHO NÚT HOME HEADER */
.home-btn {
  color: var(--primary);
  background: rgba(255, 255, 255, 0.08);
  border: 1px solid var(--panel-border);
  width: 36px;
  height: 36px;
  border-radius: 50%;
  display: flex;
  align-items: center;
  justify-content: center;
  text-decoration: none;
  font-size: 0.95rem;
  transition: all 0.2s ease;
}

.home-btn:hover {
  background: var(--primary);
  color: #fff;
  transform: scale(1.08);
  border-color: var(--primary);
}

/* ==========================================
   FIX RESPONSIVE MOBILE - TỰ ĐỘNG XUỐNG DÒNG & CUỘN NGANG
========================================== */
@media (max-width: 768px) {
  /* 1. Đổi Header thành cột (Logo ở trên, Nút ở dưới) */
  header {
    flex-direction: column;
    align-items: center;
    padding: 0.5rem 0.5rem;
    gap: 0.5rem;
  }

  .logo {
    font-size: 1rem;
  }

  /* 2. Thanh Controls rộng 100%, tự do cuộn ngang */
  .controls {
    width: 100%;
    max-width: 100%;
    justify-content: flex-start; /* Xếp sát nhau từ trái sang */
    padding: 0.4rem 0.6rem;
    gap: 0.35rem;
    overflow-x: auto; /* Cho phép cuộn ngang khi tràn */
    overflow-y: hidden;
    white-space: nowrap;
    -webkit-overflow-scrolling: touch;
  }

  /* Ẩn thanh cuộn xấu nhưng vẫn lướt ngón tay được */
  .controls::-webkit-scrollbar { 
    display: none; 
  }
  .controls { 
    -ms-overflow-style: none; 
    scrollbar-width: none; 
  }

  /* 3. Tối ưu kích thước các nút */
  .btn {
    padding: 0.35rem 0.5rem;
    font-size: 0.78rem;
    flex-shrink: 0; /* Không cho nút bị co rúm */
  }

  /* Ẩn bớt chữ "Mở PDF", chỉ chừa icon trên mobile */
  label[for="pdf-input"] span {
    display: none;
  }

  .divider {
    margin: 0 1px;
    height: 14px;
    flex-shrink: 0;
  }

  .page-info, .zoom-info {
    font-size: 0.75rem;
    min-width: 35px;
    flex-shrink: 0;
  }

  /* 4. Footer căn giữa gọn gàng ở đáy */
  .copyright-footer {
    bottom: 5px;
    right: 50%;
    transform: translateX(50%);
    font-size: 0.68rem;
    white-space: nowrap;
  }
}