:root {
  /* Colors */
  --bg-primary: #f1f5f9;
  --bg-secondary: #ffffff;
  --bg-detail: #6dee62;
  --text-primary: #0f172a;
  --text-secondary: #475569;
  --text-muted: #555555;
  --text-white: #ffffff;

  --primary-gradient-start: #031a07;
  --primary-gradient-end: #02380b;

  --accent-color: #2563eb;
  --accent-hover: #cbd5e1;
  --footer-bg: #456fd1;

  --btn-gradient-start: #0d6efd;
  --btn-gradient-end: #084298;
  --btn-detail-bg: #1c72f3;

  /* Font Sizes - Responsive Typography */
  --fs-h1: clamp(28px, 6vw, 42px);
  --fs-h2: clamp(22px, 5vw, 32px);
  --fs-h3: clamp(18px, 4vw, 24px);
  --fs-body: clamp(15px, 2vw, 18px);
  --fs-nav: clamp(14px, 1.5vw, 16px);
  --fs-logo: clamp(18px, 3vw, 24px);

  /* Spacing & Borders */
  --radius-sm: 6px;
  --radius-md: 10px;
  --radius-lg: 12px;
  --radius-xl: 14px;
  --radius-full: 40px;

  --transition: 0.3s;
  --border-color: #cbd5e1;
}

* {
  margin: 0;
  padding: 0;
  box-sizing: border-box;
}

body {
  font-family: Segoe UI, sans-serif;
  background: var(--bg-primary);
  color: var(--text-primary);
  font-size: var(--fs-body);
  line-height: 1.6;
}

/* HEADER */
header {
  position: sticky;
  top: 0;
  z-index: 9999;
  background: linear-gradient(135deg, var(--primary-gradient-start), var(--primary-gradient-end));
  padding: 15px 10px;
  color: var(--text-white);
}

nav {
  max-width: 1200px;
  margin: auto;
  display: flex;
  justify-content: space-between;
  align-items: center;
}

nav h1 {
  font-size: var(--fs-logo);
  cursor: pointer;
}

.nav-links {
  display: flex;
  align-items: center;
}

nav a {
  color: var(--text-white);
  margin: 0 10px;
  text-decoration: none;
  font-weight: 600;
  font-size: var(--fs-nav);
  transition: var(--transition);
}

nav a:hover {
  color: var(--accent-hover);
}

.menu-toggle {
  display: none;
  flex-direction: column;
  cursor: pointer;
}

.menu-toggle span {
  width: 25px;
  height: 3px;
  background-color: var(--text-white);
  margin: 2px 0;
  transition: 0.4s;
}

@media (max-width: 768px) {
  .menu-toggle {
    display: flex;
  }

  .nav-links {
    display: none;
    flex-direction: column;
    position: absolute;
    top: 60px;
    left: 0;
    width: 100%;
    background: var(--primary-gradient-start);
    padding: 20px 0;
    text-align: center;
    box-shadow: 0 5px 10px rgba(0, 0, 0, 0.2);
  }

  .nav-links.active {
    display: flex;
  }

  .nav-links a {
    margin: 8px 0;
    font-size: 1.1rem;
  }
}

/* HERO */
.hero {
  background: var(--bg-secondary);
  padding: 30px 10px;
  text-align: center;
}

.hero h2 {
  font-size: var(--fs-h1);
  line-height: 1.2;
}

.hero p {
  font-size: var(--fs-body);
  color: var(--text-secondary);
  margin-top: 10px;
}

/* SLIDER */
.slider {
  max-width: 1100px;
  margin: 20px auto;
  overflow: hidden;
}

.slides {
  display: flex;
  animation: slide 15s infinite;
}

.slide {
  min-width: 100%;
  text-align: center;
}

.slide img {
  width: 100%;
  height: 100%;
  object-fit: cover;
  border-radius: var(--radius-lg);
  box-shadow: 0 10px 20px rgba(0, 0, 0, .2);
}

@keyframes slide {
  0% {
    transform: translateX(0)
  }

  33% {
    transform: translateX(-100%)
  }

  66% {
    transform: translateX(-200%)
  }
}

/* BOOK GRID */
.books {
  max-width: 1200px;
  margin: auto;
  padding: 20px 10px;
  display: grid;
  grid-template-columns: repeat(4, 1fr);
  gap: 20px;
}

.book {
  background: var(--bg-secondary);
  padding: 15px;
  border-radius: var(--radius-xl);
  text-align: center;
  text-decoration: none;
  color: inherit;
  box-shadow: 0 10px 25px rgba(0, 0, 0, .1);
}

.book h3 {
  font-size: 1rem;
  margin-top: 10px;
  line-height: 1.3;
}

.book img {
  width: 100%;
  min-height: 180px;
  max-height: 280px;
  object-fit: cover;
  border-radius: var(--radius-md);
}

.book:hover {
  transform: translateY(-6px);
  transition: var(--transition);
}

/* RESPONSIVE */
@media(max-width:1024px) {
  .books {
    grid-template-columns: repeat(3, 1fr);
    gap: 15px;
  }
}

@media(max-width:768px) {
  .books {
    grid-template-columns: repeat(3, 1fr);
    gap: 12px;
  }
}

@media(max-width:600px) {
  .books {
    grid-template-columns: repeat(2, 1fr);
  }
}

@media(max-width:480px) {
  .books {
    grid-template-columns: repeat(2, 1fr);
    gap: 10px;
    padding: 15px 5px;
  }

  .book {
    padding: 10px;
  }

  .book h3 {
    font-size: 0.85rem;
  }

  .book img {
    min-height: 120px;
    max-height: 200px;
  }
}

/* PAGE */
.page {
  max-width: 900px;
  margin: 30px auto;
  background: var(--bg-secondary);
  padding: 30px 15px;
  border-radius: var(--radius-xl);
}

.page h2 {
  font-size: var(--fs-h2);
  margin-bottom: 20px;
}

/* FORM */
form input,
form textarea {
  width: 100%;
  padding: 12px;
  margin: 8px 0;
  border-radius: var(--radius-sm);
  border: 1px solid var(--border-color);
  font-size: 1rem;
}

form button {
  background: var(--accent-color);
  color: var(--text-white);
  border: none;
  padding: 10px 25px;
  border-radius: var(--radius-sm);
  cursor: pointer;
  font-size: 1rem;
  font-weight: 600;
}

/* FOOTER */
footer {
  background: var(--primary-gradient-start);
  color: var(--text-white);
  padding: 40px 10px 20px;
  margin-top: 50px;
}

.footer-content {
  max-width: 1200px;
  margin: auto;
  display: flex;
  justify-content: space-between;
  flex-wrap: wrap;
  gap: 30px;
  border-bottom: 1px solid rgba(255, 255, 255, 0.1);
  padding-bottom: 30px;
}

.footer-section {
  flex: 1;
  min-width: 200px;
}

.footer-section h4 {
  margin-bottom: 15px;
  font-size: 1.1rem;
  color: var(--bg-detail);
}

.footer-links {
  list-style: none;
}

.footer-links li {
  margin-bottom: 8px;
}

.footer-links a {
  color: #cbd5e1;
  text-decoration: none;
  font-size: 0.9rem;
  transition: var(--transition);
}

.footer-links a:hover {
  color: var(--text-white);
  padding-left: 5px;
}

.footer-bottom {
  text-align: center;
  padding-top: 20px;
  font-size: 0.85rem;
  color: #94a3b8;
}

/* ===== DETAIL PAGE STYLES ===== */
.detail-page {
  background-color: var(--bg-detail);
  min-height: 100vh;
  padding: 10px;
  font-family: inherit;
  color: #222;
}

.detail-page .ad-box {
  max-width: 1000px;
  margin: 15px auto;
  padding: 15px;
  background: var(--bg-secondary);
  border: 1px dashed #cccccc;
  text-align: center;
  color: #777;
  border-radius: 8px;
  font-size: 0.85rem;
}

.detail-page .detail-container {
  max-width: 1000px;
  margin: auto;
  background: var(--bg-secondary);
  padding: 20px;
  border-radius: var(--radius-xl);
  box-shadow: 0 6px 15px rgba(0, 0, 0, 0.08);
}

.all-books-btn {
  margin: 15px 0;
}

.all-books-btn a {
  display: inline-block;
  padding: 8px 16px;
  background-color: var(--btn-detail-bg);
  color: var(--text-white);
  text-decoration: none;
  font-size: clamp(16px, 3vw, 22px);
  font-weight: 600;
  border-radius: var(--radius-md);
  transition: var(--transition);
}

.detail-page .intro-text h1 {
  font-size: var(--fs-h2);
  margin-bottom: 8px;
  text-align: center;
}

.detail-page .intro-text p {
  font-size: var(--fs-body);
  line-height: 1.5;
  color: var(--text-muted);
  text-align: center;
  margin-bottom: 20px;
}

.detail-page .book-image img {
  width: 100%;
  max-height: 75vh;
  object-fit: contain;
  border-radius: var(--radius-lg);
}

.detail-page .download-area {
  display: flex;
  justify-content: center;
  margin-top: 25px;
}

.detail-page .download-btn {
  display: inline-block;
  padding: 14px 35px;
  background: linear-gradient(135deg, var(--btn-gradient-start), var(--btn-gradient-end));
  color: var(--text-white);
  text-decoration: none;
  font-size: clamp(16px, 2.5vw, 19px);
  font-weight: 600;
  border-radius: var(--radius-full);
  transition: transform 0.25s ease, box-shadow 0.25s ease;
  box-shadow: 0 8px 20px rgba(13, 110, 253, 0.3);
}

.detail-page .download-btn:hover {
  transform: translateY(-2px);
  box-shadow: 0 12px 25px rgba(13, 110, 253, 0.45);
}