:root {
  color-scheme: light;
  --bg: #f3f5f7;
  --surface: #ffffff;
  --surface-soft: #f8fafc;
  --text: #172033;
  --muted: #667085;
  --border: #dfe4ea;
  --primary: #2855d9;
  --primary-dark: #1f43ad;
  --success: #18794e;
  --success-bg: #edf9f2;
  --danger: #b42318;
  --danger-bg: #fff1f0;
  --warning-bg: #fff8e6;
  --shadow: 0 8px 24px rgb(23 32 51 / 7%);
  --radius: 14px;
}

* {
  box-sizing: border-box;
}

html {
  scroll-behavior: smooth;
}

body {
  margin: 0;
  min-width: 320px;
  min-height: 100vh;
  display: flex;
  flex-direction: column;
  color: var(--text);
  background: var(--bg);
  font-family: system-ui, -apple-system, BlinkMacSystemFont, "Segoe UI", sans-serif;
  line-height: 1.55;
  overflow-x: hidden;
  isolation: isolate;
}

/* Hai lớp nền rất nhẹ tạo chiều sâu nhưng vẫn giữ cảm giác tập trung. */
body::before,
body::after {
  content: "";
  position: fixed;
  z-index: -2;
  pointer-events: none;
}

body::before {
  inset: 0;
  background:
    radial-gradient(circle at 12% 8%, rgb(40 85 217 / 10%), transparent 28rem),
    radial-gradient(circle at 88% 78%, rgb(24 121 78 / 7%), transparent 30rem),
    linear-gradient(135deg, #f6f8fb 0%, var(--bg) 52%, #f5f7fa 100%);
}

body::after {
  inset: 0;
  z-index: -1;
  opacity: 0.22;
  background-image: radial-gradient(rgb(40 85 217 / 24%) 0.65px, transparent 0.65px);
  background-size: 18px 18px;
  mask-image: linear-gradient(to bottom, #000, transparent 72%);
}

button,
input {
  font: inherit;
}

button,
a {
  -webkit-tap-highlight-color: transparent;
}

.container {
  width: min(100% - 32px, 920px);
  margin-inline: auto;
}

.site-header {
  position: sticky;
  top: 0;
  z-index: 10;
  background: rgb(255 255 255 / 82%);
  border-bottom: 1px solid var(--border);
  backdrop-filter: blur(14px) saturate(130%);
  -webkit-backdrop-filter: blur(14px) saturate(130%);
}

.header-inner {
  min-height: 64px;
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 16px;
}

.brand {
  color: var(--text);
  font-size: 1.2rem;
  font-weight: 800;
  text-decoration: none;
}

.muted {
  color: var(--muted);
}

main.container {
  flex: 1;
  padding-block: 32px 48px;
  outline: none;
}

/* Mỗi màn hình mới xuất hiện nhẹ nhàng khi app thay nội dung. */
main > section,
main > .donate-box {
  animation: view-enter 0.42s cubic-bezier(0.22, 1, 0.36, 1) both;
}

main > section:nth-child(2) {
  animation-delay: 45ms;
}

main > section:nth-child(3),
main > .donate-box {
  animation-delay: 90ms;
}

.page-heading {
  margin-bottom: 24px;
}

.page-heading h1,
.quiz-card h2,
.question-card h2,
.result-card h2 {
  margin-top: 0;
  line-height: 1.3;
}

.page-heading h1 {
  margin-bottom: 8px;
  font-size: clamp(1.65rem, 5vw, 2.3rem);
}

.page-heading p {
  max-width: 680px;
  margin: 0;
  color: var(--muted);
}

.quiz-grid {
  display: grid;
  gap: 16px;
}

.home-tools {
  margin-bottom: 20px;
  padding: 18px;
  background: rgb(255 255 255 / 78%);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  box-shadow: var(--shadow);
  backdrop-filter: blur(10px);
}

.home-tools label {
  display: block;
  margin-bottom: 8px;
  font-size: 0.92rem;
  font-weight: 750;
}

.search-field {
  position: relative;
}

.search-field span {
  position: absolute;
  left: 14px;
  top: 50%;
  color: var(--muted);
  font-size: 1.35rem;
  line-height: 1;
  transform: translateY(-52%);
  pointer-events: none;
}

.search-field input {
  width: 100%;
  min-height: 48px;
  padding: 10px 42px;
  border: 1px solid var(--border);
  border-radius: 10px;
  outline: none;
  background: var(--surface);
  color: var(--text);
  transition: border-color 0.16s ease, box-shadow 0.16s ease;
}

.search-field input:focus {
  border-color: var(--primary);
  box-shadow: 0 0 0 4px rgb(40 85 217 / 10%);
}

.search-field input::placeholder {
  color: #98a2b3;
}

.search-summary {
  min-height: 1.4em;
  margin: 9px 0 0;
  color: var(--muted);
  font-size: 0.88rem;
}

.empty-state {
  grid-column: 1 / -1;
  box-shadow: none;
}

.pagination {
  min-height: 44px;
  display: flex;
  align-items: center;
  justify-content: center;
  gap: 14px;
  margin-top: 24px;
}

.pagination[hidden] {
  display: none;
}

.pagination span {
  color: var(--muted);
  white-space: nowrap;
}

.quiz-card,
.panel,
.question-card,
.result-card,
.status-card,
.donate-box {
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  box-shadow: var(--shadow);
}

.quiz-card {
  padding: 22px;
  display: flex;
  flex-direction: column;
  align-items: flex-start;
  position: relative;
  overflow: hidden;
  animation: card-enter 0.46s cubic-bezier(0.22, 1, 0.36, 1) both;
  transition: transform 0.22s ease, box-shadow 0.22s ease, border-color 0.22s ease;
}

.quiz-card::before {
  content: "";
  position: absolute;
  inset: 0 0 auto;
  height: 3px;
  opacity: 0;
  background: linear-gradient(90deg, var(--primary), #6f8ff5);
  transition: opacity 0.22s ease;
}

.quiz-card:nth-child(2) {
  animation-delay: 70ms;
}

.quiz-card:nth-child(3) {
  animation-delay: 140ms;
}

.quiz-card:nth-child(4) {
  animation-delay: 210ms;
}

.quiz-card:hover {
  transform: translateY(-4px);
  border-color: #cbd5ef;
  box-shadow: 0 14px 34px rgb(23 32 51 / 11%);
}

.quiz-card:hover::before {
  opacity: 1;
}

.quiz-card h2 {
  margin-bottom: 8px;
  font-size: 1.15rem;
}

.quiz-card p {
  margin: 0 0 16px;
  color: var(--muted);
}

.quiz-meta,
.history-row {
  display: flex;
  flex-wrap: wrap;
  gap: 8px 14px;
  margin-bottom: 18px;
  color: var(--muted);
  font-size: 0.9rem;
}

.history-row {
  width: 100%;
  padding: 10px 12px;
  background: var(--surface-soft);
  border-radius: 9px;
}

.quiz-card .button {
  margin-top: auto;
}

.panel,
.question-card,
.result-card {
  padding: clamp(20px, 5vw, 32px);
}

.start-details {
  margin: 20px 0;
  padding: 14px 16px;
  background: var(--surface-soft);
  border-radius: 10px;
  color: var(--muted);
}

.check-row {
  display: flex;
  align-items: center;
  gap: 11px;
  margin: 0;
  cursor: pointer;
}

.quiz-settings {
  display: grid;
  gap: 13px;
  margin: 22px 0;
  padding: 16px;
  border: 1px solid var(--border);
  border-radius: 10px;
  background: var(--surface-soft);
}

.check-row input {
  width: 19px;
  height: 19px;
  accent-color: var(--primary);
}

.button-row {
  display: flex;
  flex-wrap: wrap;
  gap: 10px;
  margin-top: 24px;
}

.button {
  min-height: 44px;
  padding: 10px 17px;
  display: inline-flex;
  align-items: center;
  justify-content: center;
  border: 1px solid transparent;
  border-radius: 9px;
  background: var(--primary);
  color: #fff;
  font-weight: 700;
  text-decoration: none;
  cursor: pointer;
  position: relative;
  overflow: hidden;
  box-shadow: 0 4px 12px rgb(40 85 217 / 18%);
  transition: background 0.15s ease, transform 0.15s ease, box-shadow 0.15s ease;
}

.button:hover {
  background: var(--primary-dark);
  box-shadow: 0 7px 16px rgb(40 85 217 / 24%);
  transform: translateY(-1px);
}

.button:active {
  transform: translateY(1px);
}

.button.secondary {
  border-color: var(--border);
  background: var(--surface);
  color: var(--text);
  box-shadow: none;
}

.button.secondary:hover {
  background: var(--surface-soft);
}

.button.danger {
  background: var(--danger);
}

.button:disabled {
  opacity: 0.48;
  cursor: not-allowed;
  transform: none;
}

.quiz-topbar {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 16px;
  margin-bottom: 10px;
}

.quiz-topbar strong {
  font-size: 0.95rem;
}

.progress {
  width: 100%;
  height: 9px;
  margin-bottom: 24px;
  overflow: hidden;
  border-radius: 999px;
  background: #e8ecf2;
}

.progress-bar {
  height: 100%;
  border-radius: inherit;
  background: linear-gradient(90deg, var(--primary), #6f8ff5, var(--primary));
  background-size: 200% 100%;
  animation: progress-glow 2.8s ease-in-out infinite;
  transition: width 0.2s ease;
}

.question-text {
  margin-bottom: 20px;
  font-size: clamp(1.08rem, 3vw, 1.3rem);
  animation: question-copy-enter 0.38s 45ms cubic-bezier(0.22, 1, 0.36, 1) both;
}

.answers {
  display: grid;
  gap: 11px;
  border: 0;
  padding: 0;
  margin: 0;
}

.answer-option {
  min-height: 54px;
  display: flex;
  align-items: flex-start;
  gap: 12px;
  padding: 14px 16px;
  border: 1px solid var(--border);
  border-radius: 10px;
  background: var(--surface);
  cursor: pointer;
  animation: answer-enter 0.36s cubic-bezier(0.22, 1, 0.36, 1) both;
  transition: border-color 0.16s ease, background 0.16s ease, transform 0.16s ease, box-shadow 0.16s ease;
}

.answer-option:nth-child(1) { animation-delay: 80ms; }
.answer-option:nth-child(2) { animation-delay: 125ms; }
.answer-option:nth-child(3) { animation-delay: 170ms; }
.answer-option:nth-child(4) { animation-delay: 215ms; }

.answer-option:hover {
  border-color: #9aabe5;
  transform: translateX(3px);
  box-shadow: 0 4px 14px rgb(23 32 51 / 6%);
}

.answer-option:has(input:checked) {
  border-color: var(--primary);
  background: #f1f5ff;
  box-shadow: 0 0 0 3px rgb(40 85 217 / 8%);
}

.answer-option:has(input:disabled) {
  cursor: default;
}

.answer-option.correct-answer,
.answer-option.correct-answer:has(input:checked) {
  border-color: var(--success);
  background: var(--success-bg);
  box-shadow: 0 0 0 3px rgb(24 121 78 / 8%);
}

.answer-option.wrong-answer,
.answer-option.wrong-answer:has(input:checked) {
  border-color: var(--danger);
  background: var(--danger-bg);
  box-shadow: 0 0 0 3px rgb(180 35 24 / 7%);
}

.instant-feedback {
  margin-top: 18px;
  padding: 16px 18px;
  border: 1px solid var(--border);
  border-left-width: 4px;
  border-radius: 10px;
  animation: feedback-enter 0.34s cubic-bezier(0.22, 1, 0.36, 1) both;
}

.instant-feedback p {
  margin: 7px 0 0;
}

.instant-feedback.feedback-correct {
  border-left-color: var(--success);
  background: var(--success-bg);
  color: #145c3d;
}

.instant-feedback.feedback-incorrect {
  border-left-color: var(--danger);
  background: var(--danger-bg);
  color: #8f1d14;
}

.answer-option input {
  flex: 0 0 auto;
  width: 18px;
  height: 18px;
  margin-top: 3px;
  accent-color: var(--primary);
}

.answer-letter {
  font-weight: 800;
}

.question-nav {
  display: flex;
  justify-content: space-between;
  gap: 10px;
  margin-top: 26px;
  animation: nav-enter 0.38s 220ms cubic-bezier(0.22, 1, 0.36, 1) both;
}

.question-card.is-next {
  animation: question-next 0.4s cubic-bezier(0.22, 1, 0.36, 1) both;
}

.question-card.is-previous {
  animation: question-previous 0.4s cubic-bezier(0.22, 1, 0.36, 1) both;
}

.question-card.is-stay {
  animation: feedback-view-enter 0.28s ease-out both;
}

.question-nav .right-actions {
  display: flex;
  gap: 10px;
}

.score-block {
  margin: 18px 0 24px;
  padding: 20px;
  text-align: center;
  border-radius: 12px;
  background: var(--surface-soft);
}

.score-number {
  display: block;
  font-size: clamp(2rem, 8vw, 3.2rem);
  font-weight: 800;
  line-height: 1.1;
  animation: score-pop 0.48s 0.12s cubic-bezier(0.22, 1, 0.36, 1) both;
}

.score-percent {
  color: var(--primary);
  font-weight: 800;
}

.result-list {
  display: grid;
  gap: 14px;
  margin-top: 26px;
}

.result-item {
  padding: 18px;
  border: 1px solid var(--border);
  border-left-width: 5px;
  border-radius: 11px;
  animation: result-enter 0.4s cubic-bezier(0.22, 1, 0.36, 1) both;
  transition: transform 0.18s ease, box-shadow 0.18s ease;
}

.result-item:hover {
  transform: translateY(-2px);
  box-shadow: 0 8px 20px rgb(23 32 51 / 7%);
}

.result-item:nth-child(2) { animation-delay: 50ms; }
.result-item:nth-child(3) { animation-delay: 100ms; }
.result-item:nth-child(4) { animation-delay: 150ms; }
.result-item:nth-child(5) { animation-delay: 200ms; }
.result-item:nth-child(n + 6) { animation-delay: 250ms; }

.donate-box {
  position: relative;
  overflow: hidden;
}

.donate-box::after {
  content: "";
  position: absolute;
  width: 130px;
  height: 130px;
  right: -55px;
  bottom: -72px;
  border-radius: 50%;
  background: rgb(255 193 7 / 9%);
}

.result-item.correct {
  border-left-color: var(--success);
  background: var(--success-bg);
}

.result-item.incorrect {
  border-left-color: var(--danger);
  background: var(--danger-bg);
}

.result-item h3 {
  margin: 0 0 10px;
  font-size: 1rem;
}

.result-item p {
  margin: 6px 0;
}

.result-status {
  font-weight: 800;
}

.correct .result-status {
  color: var(--success);
}

.incorrect .result-status {
  color: var(--danger);
}

.explanation {
  margin-top: 12px !important;
  padding-top: 12px;
  border-top: 1px solid rgb(102 112 133 / 22%);
}

.donate-box {
  margin-top: 26px;
  padding: 20px;
  background: var(--warning-bg);
}

.donate-box p {
  margin: 0 0 12px;
}

.donate-box a {
  color: var(--primary-dark);
  font-weight: 700;
}

.status-card {
  padding: 34px;
  text-align: center;
}

.status-card.error {
  border-color: #f0bbb6;
  background: var(--danger-bg);
  color: var(--danger);
}

.status-card p {
  margin: 8px 0;
}

.spinner {
  width: 30px;
  height: 30px;
  margin: 0 auto 12px;
  border: 3px solid var(--border);
  border-top-color: var(--primary);
  border-radius: 50%;
  animation: spin 0.8s linear infinite;
}

.site-footer {
  padding: 22px 0;
  border-top: 1px solid var(--border);
  color: var(--muted);
  font-size: 0.86rem;
  text-align: center;
}

@keyframes spin {
  to { transform: rotate(360deg); }
}

@keyframes view-enter {
  from {
    opacity: 0;
    transform: translateY(9px);
  }
  to {
    opacity: 1;
    transform: translateY(0);
  }
}

@keyframes card-enter {
  from {
    opacity: 0;
    transform: translateY(14px) scale(0.99);
  }
  to {
    opacity: 1;
    transform: translateY(0) scale(1);
  }
}

@keyframes result-enter {
  from {
    opacity: 0;
    transform: translateX(-8px);
  }
  to {
    opacity: 1;
    transform: translateX(0);
  }
}

@keyframes score-pop {
  from {
    opacity: 0;
    transform: scale(0.86);
  }
  to {
    opacity: 1;
    transform: scale(1);
  }
}

@keyframes progress-glow {
  0%, 100% { background-position: 0% 50%; }
  50% { background-position: 100% 50%; }
}

@keyframes question-next {
  from {
    opacity: 0;
    transform: translateX(18px) scale(0.995);
  }
  to {
    opacity: 1;
    transform: translateX(0) scale(1);
  }
}

@keyframes question-previous {
  from {
    opacity: 0;
    transform: translateX(-18px) scale(0.995);
  }
  to {
    opacity: 1;
    transform: translateX(0) scale(1);
  }
}

@keyframes question-copy-enter {
  from {
    opacity: 0;
    transform: translateY(5px);
  }
  to {
    opacity: 1;
    transform: translateY(0);
  }
}

@keyframes answer-enter {
  from {
    opacity: 0;
    transform: translateY(8px);
  }
  to {
    opacity: 1;
    transform: translateY(0);
  }
}

@keyframes nav-enter {
  from {
    opacity: 0;
    transform: translateY(7px);
  }
  to {
    opacity: 1;
    transform: translateY(0);
  }
}

@keyframes feedback-enter {
  from {
    opacity: 0;
    transform: translateY(-5px);
  }
  to {
    opacity: 1;
    transform: translateY(0);
  }
}

@keyframes feedback-view-enter {
  from { opacity: 0.82; }
  to { opacity: 1; }
}

@media (min-width: 680px) {
  .quiz-grid {
    grid-template-columns: repeat(2, minmax(0, 1fr));
  }
}

@media (max-width: 560px) {
  .container {
    width: min(100% - 24px, 920px);
  }

  main.container {
    padding-top: 22px;
  }

  .question-nav,
  .question-nav .right-actions {
    display: grid;
    grid-template-columns: 1fr 1fr;
  }

  .question-nav {
    grid-template-columns: 1fr;
  }

  .question-nav .button,
  .button-row .button {
    flex: 1 1 100%;
  }

  .quiz-card:hover {
    transform: none;
  }

  .answer-option:hover {
    transform: none;
  }

  .result-item:hover {
    transform: none;
  }

  .home-tools {
    padding: 14px;
  }

  .pagination {
    display: grid;
    grid-template-columns: 1fr 1fr;
  }

  .pagination span {
    grid-column: 1 / -1;
    grid-row: 1;
    text-align: center;
  }
}

@media (prefers-reduced-motion: reduce) {
  *,
  *::before,
  *::after {
    scroll-behavior: auto !important;
    transition: none !important;
    animation-duration: 0.01ms !important;
    animation-iteration-count: 1 !important;
  }
}