body {
  margin: 0;
  font-family: "Roboto Slab", "Times New Roman", Times, serif;
  background: url("/assets/img/bg.jpg") center center/cover no-repeat fixed;
  position: relative;
  color: #222;
}

button {
  font-family: "Roboto Slab", "Times New Roman", Times, serif;
}
body::before {
  content: "";
  position: fixed;
  inset: 0;
  background: rgba(255, 255, 255, 0.85); /* 0.5 = 50% mờ */
  z-index: -1;
  pointer-events: none;
}
.header {
  padding: 24px 16px 16px 16px;
}
.logo {
  width: 150px;
  height: 150px;
  object-fit: contain;
  margin-bottom: 8px;
}
.logo.small {
  width: 48px;
  height: 48px;
  margin-bottom: 0;
}
.school-name {
  font-size: 2.2rem;
  font-weight: bold;
  letter-spacing: 2px;
}
.hero {
  display: flex;
  flex-direction: column;
  align-items: center;
  margin: 32px 0 0 0;
}
.hero-img {
  width: 90vw;
  max-width: 600px;
  border-radius: 18px;
  box-shadow: 0 4px 24px rgba(59, 89, 152, 0.12);
  margin-bottom: 32px;
  transition: transform 0.5s cubic-bezier(0.4, 2, 0.6, 1);
}
.hero-img:hover {
  transform: scale(1.03) rotate(-1deg);
}
.start-btn {
  background: #3b5998;
  color: #fff;
  font-size: 1.5rem;
  padding: 16px 48px;
  border: none;
  border-radius: 32px;
  cursor: pointer;
  font-weight: bold;
  box-shadow: 0 2px 8px rgba(59, 89, 152, 0.12);
  transition: background 0.3s, transform 0.2s;
}
.start-btn:hover {
  background: #2d4373;
  transform: scale(1.05);
}
.topics-grid {
  display: grid;
  grid-template-columns: repeat(
    4,
    minmax(0, 1fr)
  ); /* Luôn 4 cột, không co giãn quá mức */
  gap: 40px;
  padding: 56px 5vw 0 5vw;
  align-items: stretch;
  position: relative;
  justify-items: center; /* căn giữa các item nếu thiếu */
}
.topic-card {
  border-radius: 18px;
  padding: 0;
  text-align: center;
  cursor: pointer;
  flex: 1 1 auto;
  display: flex;
  flex-direction: column;
  justify-content: center;
  background: white;
}

.topic-card:before {
  content: "";
  z-index: -1;
  position: absolute;
  top: 0;
  right: 0;
  bottom: 0;
  left: 0;
  background: linear-gradient(to left, #c9a063 -33%, #3b5998 200%);
  transform: translate3d(3px, 3px, 0) scale(1);
  filter: blur(0px);
  opacity: var(0.7);
  transition: opacity 0.3s;
  border-radius: inherit;
}

@keyframes slideInUp {
  from {
    opacity: 0;
    transform: translateY(50px);
  }
  to {
    opacity: 1;
    transform: translateY(0);
  }
}

.topic-card-wrapper:hover {
  box-shadow: 0 12px 36px rgba(59, 89, 152, 0.25);
  border-color: #c9a063;
  transform: scale(1.04) rotate(-1deg); /* bỏ translateY */
  transition: transform 0.3s ease, box-shadow 0.3s ease, border-color 0.3s ease;
}

/* .topic-card::after {
    content: "";
    position: absolute;
    bottom: 0;
    left: 0;
    right: 0;
    height: 5px;
    background: linear-gradient(90deg, #c9a063 0%, #3b5998 100%);
    opacity: 0.7;
} */
.topic-icon {
  width: 100%;
  height: 200px;
  display: block;
  padding: 0;
  margin: 0;
  border-radius: 0;
  max-height: none;
  object-fit: cover;
}
.topic-card h2 {
  font-size: 1.5rem;
  color: #3b5998;
  margin: 0;
  font-weight: bold;
  padding: 20px 10px;
}
.topic-detail main {
  max-width: 800px;
  margin: 0 auto;
  padding: 32px 16px;
}
#topic-title {
  color: #3b5998;
  font-size: 2rem;
  margin-top: 12px;
}
.topic-content {
  background: #fff;
  border-radius: 16px;
  box-shadow: 0 2px 12px rgba(59, 89, 152, 0.08);
  padding: 32px 24px;
  font-size: 1.2rem;
  color: #222;
  margin-bottom: 32px;
  line-height: 1.7;
}
.back-btn {
  color: #fff;
  font-size: 1.1rem;
  padding: 12px 32px;
  border: none;
  border-radius: 24px;
  cursor: pointer;
  font-weight: bold;
  box-shadow: 0 2px 8px rgba(59, 89, 152, 0.1);
  transition: background 0.3s, transform 0.2s;
}
.back-btn:hover {
  background: #2d4373;
  transform: scale(1.04);
}
.start-btn,
.back-btn {
  background: linear-gradient(90deg, #3b5998 60%, #c9a063 100%);
  color: #fff;
  font-size: 1.5rem;
  padding: 16px 48px;
  border: none;
  border-radius: 32px;
  cursor: pointer;
  font-weight: bold;
  box-shadow: 0 2px 8px rgba(59, 89, 152, 0.12);
  transition: background 0.3s, transform 0.2s, box-shadow 0.3s;
  position: relative;
  overflow: hidden;
}
.start-btn:hover,
.back-btn:hover {
  background: linear-gradient(90deg, #c9a063 0%, #3b5998 100%);
  color: #fff;
  box-shadow: 0 4px 24px #c9a06355;
  transform: scale(1.07);
}
.decor-icon {
  width: 48px;
  height: 48px;
  margin-bottom: 8px;
  opacity: 0.7;
  display: block;
  margin-left: auto;
  margin-right: auto;
}
.topics-grid {
  gap: 40px;
  padding: 56px 5vw 0 5vw;
}
.decorative-corner {
  position: fixed;
  right: 2vw;
  bottom: 2vw;
  width: 96px;
  height: 96px;
  opacity: 0.18;
  z-index: 1;
  pointer-events: none;
}
.header,
.main,
.topics-grid,
.topic-content {
  position: relative;
  z-index: 2;
}
.topic-card-wrapper {
  width: 100%;
  position: relative;
  transition: box-shadow 0.3s, transform 0.3s, border-color 0.3s,
    background 0.3s;
  border-radius: 18px;
  border: 2px solid #3b5998;
  box-shadow: 0 4px 24px rgba(59, 89, 152, 0.1);
  margin-bottom: 16px;
  height: 100%;
  display: flex;
  flex-direction: column;
  background-color: white;
  min-height: 165px;
}
.topic-card-wrapper:hover {
  box-shadow: 0 12px 36px rgba(59, 89, 152, 0.25);
  transform: translateY(-10px) scale(1.04) rotate(-1deg);
  border-color: #c9a063;
  background: #f9f6f2;
}
.topic-card-wrapper:hover .card-lotus {
  filter: brightness(1.1) drop-shadow(0 2px 8px #c9a06388);
}
.card-lotus {
  position: absolute;
  width: 35px;
  height: 35px;
  transform: rotate(45deg);
  pointer-events: none;
  z-index: 3;
  top: -15px;
  right: -15px;
}
/* Đặt vị trí cho từng hoa sen tương ứng với từng card */
.topics-grid > .card-lotus:nth-of-type(2) {
  grid-row: 1;
  grid-column: 1;
  top: 8px;
  right: 8px;
}
.topics-grid > .card-lotus:nth-of-type(4) {
  grid-row: 1;
  grid-column: 2;
  top: 8px;
  right: 8px;
}
.topics-grid > .card-lotus:nth-of-type(6) {
  grid-row: 1;
  grid-column: 3;
  top: 8px;
  right: 8px;
}
.topics-grid > .card-lotus:nth-of-type(8) {
  grid-row: 1;
  grid-column: 4;
  top: 8px;
  right: 8px;
}
.topics-grid > .card-lotus:nth-of-type(10) {
  grid-row: 2;
  grid-column: 1;
  top: 8px;
  right: 8px;
}
.topics-grid > .card-lotus:nth-of-type(12) {
  grid-row: 2;
  grid-column: 2;
  top: 8px;
  right: 8px;
}
.topics-grid > .card-lotus:nth-of-type(14) {
  grid-row: 2;
  grid-column: 3;
  top: 8px;
  right: 8px;
}
.topics-grid > .card-lotus:nth-of-type(16) {
  grid-row: 2;
  grid-column: 4;
  top: 8px;
  right: 8px;
}

/* === HERO SECTION LAYOUT === */
.hero-section {
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: space-between;
  min-height: 100vh;
  padding: 30px 100px;
  box-sizing: border-box;
}
.hero-left {
  flex: 0 0 340px;
  display: flex;
  align-items: flex-start;
  justify-content: center;
  padding-left: 5vw;
}
.school-img {
  object-fit: cover;
  width: 100%;
  border-radius: 24px;
  box-shadow: 0 4px 32px rgba(59, 89, 152, 0.13);
}
.hero-right {
  display: flex;
  flex-direction: column;
  margin-top: 50px;
}
.school-name {
  font-size: 3.5em;
  font-weight: bold;
  color: #222;
  letter-spacing: 1px;
  white-space: nowrap;
  margin-left: 50px;
  text-align: center;
}
.school-desc {
  font-size: 1.3rem;
  color: #444;
  margin-bottom: 32px;
  line-height: 1.7;
}
.hero-buttons {
  display: flex;
  gap: 18px;
}
.hero-btn {
  background: linear-gradient(90deg, #3b5998 60%, #c9a063 100%);
  color: white;
  font-size: 1.1rem;
  padding: 14px 32px;
  border: none;
  border-radius: 14px;
  font-weight: 600;
  cursor: pointer;
  box-shadow: 0 2px 8px rgba(59, 89, 152, 0.1);
  transition: background 0.2s, color 0.2s, transform 0.2s;
}
.hero-btn:hover {
  background: linear-gradient(90deg, #c9a063 60%, #3b5998 100%);
  transform: translateY(-2px) scale(1.04);
}

/* === DECORATIVE SQUARES === */
.decor-squares {
  position: absolute;
  right: 3vw;
  top: 40px;
  display: grid;
  grid-template-columns: repeat(3, 64px);
  grid-template-rows: repeat(3, 64px);
  gap: 12px;
  z-index: 2;
}
.square {
  width: 64px;
  height: 64px;
  border-radius: 18px;
  box-shadow: 0 2px 8px rgba(59, 89, 152, 0.1);
}
.square.pattern {
  background: repeating-linear-gradient(
    135deg,
    #1a237e 0 8px,
    #ffb300 8px 16px,
    #1a237e 16px 24px,
    #fff 24px 32px
  );
  background-size: 32px 32px;
  border: 2px solid #3b5998;
}
.square.yellow {
  background: #ffb300;
  border: 2px solid #ffb300;
}

/* === FOOTER YEAR === */
.footer {
  position: fixed;
  left: 32px;
  bottom: 24px;
  z-index: 10;
}
.year {
  font-size: 1.1rem;
  color: #222;
  opacity: 0.7;
  font-weight: 500;
}

/* === BACKGROUND PATTERN === */
.background-pattern {
  display: none;
}

.logo-container {
  display: flex;
  justify-content: center;
  align-items: center;
}
.hero-top {
  display: flex;
  align-items: center;
  justify-content: center;
  gap: 18px;
}
.hero-middle {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 50px;
}

/* Xóa decor-squares và square */
.decor-squares,
.square,
.square.pattern,
.square.yellow {
  display: none !important;
}

.header h1 {
  text-align: center;
  color: #3b5998;
}

.heading-decor {
  width: 120px;
  height: auto;
  display: inline-block;
  vertical-align: middle;
  margin: 0 12px;
}
@media (max-width: 700px) {
  .heading-decor {
    display: none;
  }
}
.header {
  display: flex;
  align-items: center;
  justify-content: center;
  gap: 18px;
  margin-bottom: 30px;
}
.heading-decor-ptt {
  width: 200px;
  height: auto;
  display: inline-block;
  vertical-align: middle;
  margin: 0 12px;
}
.ptt-title {
  color: #3b5998;
  font-size: 2.7em;
  margin: 0 8px;
  text-align: center;
  font-family: "Libre Bodoni", serif;
}

.side-buttons {
  position: fixed;
  top: 50%;
  right: 0;
  transform: translateY(-50%);
  display: flex;
  flex-direction: column;
  gap: 0;
  z-index: 1000;
  box-shadow: 0 2px 8px rgba(0, 0, 0, 0.15);
  border-radius: 20px 0 0 20px;
}
.side-btn {
  background: linear-gradient(90deg, #c9a063 0%, #3b5998 100%);
  border: none;
  border-radius: 0;
  width: 56px;
  height: 56px;
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: 1.7rem;
  color: #fff;
  cursor: pointer;
  transition: filter 0.2s;
  box-shadow: none;
}
.side-buttons > .side-btn:first-child {
  border-radius: 20px 0 0 0;
}
.sound-control-container > .side-btn:first-child {
  border-radius: 0 0 0 20px;
}
.side-btn:hover {
  filter: brightness(1.15) contrast(1.1);
  background: linear-gradient(90deg, #3b5998 0%, #c9a063 100%);
}

.side-btn.muted {
  opacity: 0.6;
  filter: grayscale(0.5);
}

.side-btn.muted:hover {
  filter: grayscale(0.5) brightness(1.15) contrast(1.1);
}

/* === VOLUME CONTROL STYLES === */
.sound-control-container {
  position: relative;
  display: flex;
  flex-direction: column;
  gap: 0;
}

.volume-control {
  position: absolute;
  top: 100%;
  background: linear-gradient(180deg, #c9a063 0%, #3b5998 100%);
  border-radius: 20px;
  padding: 16px;
  box-shadow: 0 4px 16px rgba(59, 89, 152, 0.2);
  opacity: 0;
  visibility: hidden;
  transition: all 0.3s cubic-bezier(0.4, 0, 0.2, 1);
  z-index: 1001;
}

.sound-control-container:hover .volume-control {
  opacity: 1;
  visibility: visible;
}

.volume-slider-container {
  display: flex;
  flex-direction: column;
  gap: 8px;
  align-items: center;
  height: 100%;
  justify-content: center;
}

.volume-slider {
  -webkit-appearance: none;
  appearance: none;
  width: 6px;
  height: 80px;
  border-radius: 3px;
  background: rgba(255, 255, 255, 0.3);
  outline: none;
  cursor: pointer;
  transition: background 0.2s;
  writing-mode: bt-lr; /* IE */
  -webkit-appearance: slider-vertical; /* WebKit */
}

.volume-slider:hover {
  background: rgba(255, 255, 255, 0.5);
}

.volume-slider::-webkit-slider-thumb {
  -webkit-appearance: none;
  appearance: none;
  width: 18px;
  height: 18px;
  border-radius: 50%;
  background: white;
  cursor: pointer;
  box-shadow: 0 2px 6px rgba(0, 0, 0, 0.2);
  transition: all 0.2s;
}

.volume-slider::-webkit-slider-thumb:hover {
  transform: scale(1.1);
  box-shadow: 0 3px 8px rgba(0, 0, 0, 0.3);
}

.volume-slider::-moz-range-thumb {
  width: 18px;
  height: 18px;
  border-radius: 50%;
  background: white;
  cursor: pointer;
  border: none;
  box-shadow: 0 2px 6px rgba(0, 0, 0, 0.2);
  transition: all 0.2s;
}

.volume-slider::-moz-range-thumb:hover {
  transform: scale(1.1);
  box-shadow: 0 3px 8px rgba(0, 0, 0, 0.3);
}

.volume-slider::-webkit-slider-track {
  background: rgba(255, 255, 255, 0.3);
  border-radius: 3px;
  width: 6px;
}

.volume-slider::-moz-range-track {
  background: rgba(255, 255, 255, 0.3);
  border-radius: 3px;
  width: 6px;
  border: none;
}

.hero-bottom {
  width: 100%;
  text-align: right;
  font-size: 0.9rem;
  margin-top: 80px;
}

@media (max-width: 1100px) {
  .topics-grid {
    grid-template-columns: repeat(2, minmax(0, 1fr));
  }
}
@media (max-width: 700px) {
  .topics-grid {
    grid-template-columns: 1fr;
  }
}

/* Responsive cho màn hình <= 880px */
@media (max-width: 880px) {
  .hero-section {
    padding: 24px 10vw;
    min-height: unset;
  }
  .hero-middle {
    grid-template-columns: 1fr;
    gap: 32px;
  }
  .school-img {
    width: 100%;
    max-width: 400px;
    margin: 0 auto;
    display: block;
  }
  .hero-right {
    margin-top: 0;
    align-items: center;
    text-align: center;
  }
  .school-name {
    font-size: 2em;
    margin-left: 0;
    white-space: normal;
  }
  .hero-top {
    flex-direction: column;
    gap: 10px;
  }
  .hero-bottom {
    text-align: center;
    margin-top: 40px;
    font-size: 0.95rem;
  }
  .background-pattern {
    display: none;
  }
  .logo-container {
    justify-content: center;
  }
  .school-desc {
    font-size: 1.1rem;
    margin-bottom: 24px;
  }
  .hero-buttons {
    flex-direction: column;
    gap: 12px;
    align-items: center;
  }
  .header {
    flex-direction: column;
    margin-bottom: 0;
  }
  .topics-grid {
    padding-top: 30px;
  }
  .heading-decor-ptt:first-child {
    display: none;
  }

  /* Volume control responsive adjustments */
  .volume-control {
    left: 0;
    min-height: 100px;
    padding: 12px 16px 12px 10px;
    width: 35px;
  }

  .volume-slider {
    height: 70px;
    width: 5px;
  }

  .volume-slider::-webkit-slider-thumb {
    width: 16px;
    height: 16px;
  }

  .volume-slider::-moz-range-thumb {
    width: 16px;
    height: 16px;
  }

  .volume-labels {
    font-size: 0.65rem;
    right: -20px;
    height: 70px;
  }

  .volume-min,
  .volume-max {
    font-size: 0.6rem;
  }
}

.topic-content img {
  width: 100%;
  border-radius: 16px;
  box-shadow: 0 2px 12px rgba(59, 89, 152, 0.08);
}