/* ============================================================
   A-Level CS Revision Quiz – Core Styles
   ============================================================ */

/* ---- Reset & Base ---- */
*, *::before, *::after {
  box-sizing: border-box;
  margin: 0;
  padding: 0;
}

:root {
  --primary:   #4f46e5;
  --primary-dark: #3730a3;
  --accent:    #06b6d4;
  --success:   #16a34a;
  --danger:    #dc2626;
  --warning:   #d97706;
  --bg:        #0f172a;
  --bg-card:   #1e293b;
  --bg-card2:  #263548;
  --text:      #f1f5f9;
  --text-muted:#94a3b8;
  --border:    #334155;
  --radius:    12px;
  --shadow:    0 4px 24px rgba(0,0,0,.4);
  --transition: 0.2s ease;
}

html { scroll-behavior: smooth; }

body {
  font-family: 'Segoe UI', system-ui, -apple-system, sans-serif;
  background: var(--bg);
  color: var(--text);
  min-height: 100vh;
  line-height: 1.6;
}

a { color: var(--accent); text-decoration: none; }
a:hover { text-decoration: underline; }

/* ---- Layout ---- */
.container {
  max-width: 1100px;
  margin: 0 auto;
  padding: 0 1.5rem;
}

/* ---- Header / Nav ---- */
header {
  background: var(--bg-card);
  border-bottom: 1px solid var(--border);
  position: sticky;
  top: 0;
  z-index: 100;
}

.nav {
  display: flex;
  align-items: center;
  justify-content: space-between;
  height: 64px;
  gap: 1rem;
}

.nav-brand {
  display: flex;
  align-items: center;
  gap: .6rem;
  font-size: 1.15rem;
  font-weight: 700;
  color: var(--text);
  cursor: pointer;
}

.nav-brand span.logo {
  font-size: 1.5rem;
}

.nav-actions {
  display: flex;
  align-items: center;
  gap: .75rem;
}

/* ---- Buttons ---- */
.btn {
  display: inline-flex;
  align-items: center;
  gap: .4rem;
  padding: .55rem 1.2rem;
  border-radius: 8px;
  font-size: .9rem;
  font-weight: 600;
  cursor: pointer;
  border: none;
  transition: all var(--transition);
  white-space: nowrap;
}

.btn-primary {
  background: var(--primary);
  color: #fff;
}
.btn-primary:hover { background: var(--primary-dark); transform: translateY(-1px); }

.btn-secondary {
  background: var(--bg-card2);
  color: var(--text);
  border: 1px solid var(--border);
}
.btn-secondary:hover { background: var(--border); }

.btn-success {
  background: var(--success);
  color: #fff;
}
.btn-success:hover { filter: brightness(1.1); }

.btn-danger {
  background: var(--danger);
  color: #fff;
}
.btn-danger:hover { filter: brightness(1.1); }

.btn-lg {
  padding: .8rem 2rem;
  font-size: 1rem;
  border-radius: 10px;
}

.btn-sm {
  padding: .35rem .8rem;
  font-size: .8rem;
}

/* ---- Views (SPA pages) ---- */
.view { display: none; }
.view.active { display: block; }

/* ---- Hero Section ---- */
.hero {
  background: linear-gradient(135deg, #1e1b4b 0%, #0c1445 40%, #0f172a 100%);
  padding: 5rem 0 4rem;
  text-align: center;
  border-bottom: 1px solid var(--border);
}

.hero-badge {
  display: inline-block;
  background: rgba(79,70,229,.25);
  color: #a5b4fc;
  border: 1px solid rgba(79,70,229,.4);
  padding: .3rem 1rem;
  border-radius: 999px;
  font-size: .8rem;
  font-weight: 600;
  letter-spacing: .05em;
  text-transform: uppercase;
  margin-bottom: 1.5rem;
}

.hero h1 {
  font-size: clamp(2rem, 5vw, 3.5rem);
  font-weight: 800;
  line-height: 1.15;
  margin-bottom: 1rem;
  background: linear-gradient(90deg, #e0e7ff, #c7d2fe, #a5b4fc);
  -webkit-background-clip: text;
  -webkit-text-fill-color: transparent;
  background-clip: text;
}

.hero p {
  font-size: 1.1rem;
  color: var(--text-muted);
  max-width: 580px;
  margin: 0 auto 2.5rem;
}

.hero-stats {
  display: flex;
  justify-content: center;
  gap: 2.5rem;
  flex-wrap: wrap;
  margin-top: 3rem;
}

.stat-item {
  text-align: center;
}

.stat-item .stat-value {
  font-size: 2rem;
  font-weight: 800;
  color: var(--accent);
}

.stat-item .stat-label {
  font-size: .8rem;
  color: var(--text-muted);
  text-transform: uppercase;
  letter-spacing: .05em;
}

/* ---- Section ---- */
section { padding: 3.5rem 0; }

.section-header {
  display: flex;
  align-items: center;
  justify-content: space-between;
  margin-bottom: 2rem;
  flex-wrap: wrap;
  gap: 1rem;
}

.section-title {
  font-size: 1.5rem;
  font-weight: 700;
}

.section-subtitle {
  color: var(--text-muted);
  font-size: .95rem;
  margin-top: .3rem;
}

/* ---- Topic Grid ---- */
.topics-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(260px, 1fr));
  gap: 1.25rem;
}

.topic-card {
  background: var(--bg-card);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 1.5rem;
  cursor: pointer;
  transition: all var(--transition);
  position: relative;
  overflow: hidden;
}

.topic-card::before {
  content: '';
  position: absolute;
  top: 0; left: 0;
  width: 4px;
  height: 100%;
  background: var(--topic-color, var(--primary));
  border-radius: 4px 0 0 4px;
}

.topic-card:hover {
  border-color: var(--topic-color, var(--primary));
  transform: translateY(-3px);
  box-shadow: var(--shadow);
}

.topic-icon {
  font-size: 2rem;
  margin-bottom: .75rem;
  display: block;
}

.topic-name {
  font-size: 1.05rem;
  font-weight: 700;
  margin-bottom: .4rem;
}

.topic-desc {
  font-size: .82rem;
  color: var(--text-muted);
  line-height: 1.5;
}

.topic-meta {
  display: flex;
  align-items: center;
  justify-content: space-between;
  margin-top: 1rem;
  font-size: .8rem;
  color: var(--text-muted);
}

.topic-badge {
  display: inline-flex;
  align-items: center;
  gap: .3rem;
  background: rgba(79,70,229,.15);
  color: #a5b4fc;
  padding: .2rem .6rem;
  border-radius: 999px;
  font-size: .75rem;
  font-weight: 600;
}

.topic-progress-bar {
  height: 4px;
  background: var(--border);
  border-radius: 4px;
  margin-top: .75rem;
  overflow: hidden;
}

.topic-progress-fill {
  height: 100%;
  background: var(--topic-color, var(--primary));
  border-radius: 4px;
  transition: width .4s ease;
}

/* ---- Progress Dashboard ---- */
.progress-overview {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(200px, 1fr));
  gap: 1rem;
  margin-bottom: 2.5rem;
}

.progress-card {
  background: var(--bg-card);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 1.25rem;
  text-align: center;
}

.progress-card .pc-value {
  font-size: 2rem;
  font-weight: 800;
  color: var(--accent);
}

.progress-card .pc-label {
  font-size: .8rem;
  color: var(--text-muted);
  margin-top: .25rem;
}

/* ---- Quiz View ---- */
.quiz-header {
  display: flex;
  align-items: center;
  justify-content: space-between;
  margin-bottom: 2rem;
  flex-wrap: wrap;
  gap: 1rem;
}

.quiz-info {
  display: flex;
  align-items: center;
  gap: 1rem;
}

.quiz-topic-badge {
  display: inline-flex;
  align-items: center;
  gap: .4rem;
  font-size: .9rem;
  font-weight: 700;
  color: var(--accent);
}

.quiz-progress-text {
  font-size: .9rem;
  color: var(--text-muted);
}

.quiz-score-display {
  font-size: .9rem;
  font-weight: 600;
  color: var(--text);
}

/* Timer */
.quiz-timer {
  display: flex;
  align-items: center;
  gap: .4rem;
  font-size: 1rem;
  font-weight: 700;
  color: var(--accent);
  background: rgba(6,182,212,.1);
  padding: .4rem .9rem;
  border-radius: 8px;
  border: 1px solid rgba(6,182,212,.2);
}

.quiz-timer.warning { color: var(--warning); background: rgba(217,119,6,.1); border-color: rgba(217,119,6,.3); }
.quiz-timer.danger  { color: var(--danger);  background: rgba(220,38,38,.1);  border-color: rgba(220,38,38,.3); }

/* Progress bar */
.quiz-progress-bar {
  height: 6px;
  background: var(--border);
  border-radius: 6px;
  margin-bottom: 2rem;
  overflow: hidden;
}

.quiz-progress-fill {
  height: 100%;
  background: linear-gradient(90deg, var(--primary), var(--accent));
  border-radius: 6px;
  transition: width .35s ease;
}

/* Question card */
.question-card {
  background: var(--bg-card);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 2rem;
  margin-bottom: 1.5rem;
  box-shadow: var(--shadow);
}

.question-number {
  font-size: .8rem;
  text-transform: uppercase;
  letter-spacing: .08em;
  color: var(--text-muted);
  margin-bottom: .75rem;
}

.question-text {
  font-size: 1.15rem;
  font-weight: 600;
  line-height: 1.55;
  margin-bottom: 1.75rem;
}

/* Options */
.options-list {
  list-style: none;
  display: flex;
  flex-direction: column;
  gap: .75rem;
}

.option-btn {
  width: 100%;
  text-align: left;
  background: var(--bg-card2);
  border: 1.5px solid var(--border);
  color: var(--text);
  border-radius: 10px;
  padding: .95rem 1.25rem;
  cursor: pointer;
  font-size: .95rem;
  transition: all var(--transition);
  display: flex;
  align-items: center;
  gap: .85rem;
}

.option-btn:hover:not(:disabled) {
  border-color: var(--primary);
  background: rgba(79,70,229,.1);
  transform: translateX(4px);
}

.option-btn .option-letter {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  width: 28px;
  height: 28px;
  border-radius: 50%;
  background: var(--border);
  font-size: .8rem;
  font-weight: 700;
  flex-shrink: 0;
  transition: all var(--transition);
}

.option-btn:hover:not(:disabled) .option-letter {
  background: var(--primary);
  color: #fff;
}

.option-btn.correct {
  border-color: var(--success);
  background: rgba(22,163,74,.15);
}
.option-btn.correct .option-letter {
  background: var(--success);
  color: #fff;
}

.option-btn.incorrect {
  border-color: var(--danger);
  background: rgba(220,38,38,.15);
}
.option-btn.incorrect .option-letter {
  background: var(--danger);
  color: #fff;
}

.option-btn:disabled { cursor: default; }

/* Explanation */
.explanation-box {
  display: none;
  background: rgba(6,182,212,.07);
  border: 1px solid rgba(6,182,212,.25);
  border-radius: 10px;
  padding: 1rem 1.25rem;
  margin-top: 1.25rem;
  font-size: .9rem;
  line-height: 1.65;
  color: var(--text);
}

.explanation-box.show { display: block; }

.explanation-box strong {
  color: var(--accent);
  display: block;
  margin-bottom: .3rem;
  font-size: .8rem;
  text-transform: uppercase;
  letter-spacing: .05em;
}

/* Quiz navigation */
.quiz-nav {
  display: flex;
  justify-content: flex-end;
  gap: .75rem;
  margin-top: 1.5rem;
}

/* ---- Results View ---- */
.results-card {
  background: var(--bg-card);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 2.5rem;
  text-align: center;
  max-width: 600px;
  margin: 3rem auto;
}

.results-emoji {
  font-size: 4rem;
  margin-bottom: 1rem;
}

.results-title {
  font-size: 1.8rem;
  font-weight: 800;
  margin-bottom: .5rem;
}

.results-subtitle {
  color: var(--text-muted);
  margin-bottom: 2rem;
}

.results-score-ring {
  position: relative;
  display: inline-flex;
  align-items: center;
  justify-content: center;
  width: 140px;
  height: 140px;
  margin: 0 auto 2rem;
}

.results-score-ring svg {
  position: absolute;
  top: 0; left: 0;
  transform: rotate(-90deg);
}

.score-circle-bg {
  fill: none;
  stroke: var(--border);
  stroke-width: 8;
}

.score-circle-fill {
  fill: none;
  stroke: var(--accent);
  stroke-width: 8;
  stroke-linecap: round;
  transition: stroke-dashoffset 1s ease;
}

.score-text {
  text-align: center;
  z-index: 1;
}

.score-percent {
  font-size: 2rem;
  font-weight: 800;
  color: var(--accent);
  display: block;
}

.score-fraction {
  font-size: .85rem;
  color: var(--text-muted);
}

.results-breakdown {
  display: flex;
  justify-content: center;
  gap: 2rem;
  margin-bottom: 2rem;
  flex-wrap: wrap;
}

.rb-item { text-align: center; }
.rb-value { font-size: 1.5rem; font-weight: 800; }
.rb-label { font-size: .8rem; color: var(--text-muted); }

.results-actions {
  display: flex;
  justify-content: center;
  gap: 1rem;
  flex-wrap: wrap;
}

/* ---- Review List ---- */
.review-list {
  display: flex;
  flex-direction: column;
  gap: 1.25rem;
  margin-top: 2rem;
}

.review-item {
  background: var(--bg-card);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 1.25rem 1.5rem;
}

.review-item.review-correct { border-left: 4px solid var(--success); }
.review-item.review-incorrect { border-left: 4px solid var(--danger); }

.review-q {
  font-weight: 600;
  margin-bottom: .6rem;
}

.review-answers {
  font-size: .88rem;
  color: var(--text-muted);
}

.review-correct-ans { color: var(--success); font-weight: 600; }
.review-incorrect-ans { color: var(--danger); text-decoration: line-through; }

.review-explanation {
  font-size: .85rem;
  color: var(--text-muted);
  margin-top: .6rem;
  padding-top: .6rem;
  border-top: 1px solid var(--border);
}

/* ---- Progress View ---- */
.topic-progress-table {
  width: 100%;
  border-collapse: collapse;
}

.topic-progress-table th,
.topic-progress-table td {
  text-align: left;
  padding: .9rem 1rem;
  font-size: .9rem;
  border-bottom: 1px solid var(--border);
}

.topic-progress-table th {
  color: var(--text-muted);
  font-weight: 600;
  text-transform: uppercase;
  font-size: .75rem;
  letter-spacing: .06em;
  background: var(--bg-card);
}

.topic-progress-table tr:last-child td { border-bottom: none; }
.topic-progress-table tr:hover td { background: rgba(255,255,255,.02); }

.table-wrapper {
  background: var(--bg-card);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  overflow: hidden;
}

.mini-bar {
  display: flex;
  align-items: center;
  gap: .6rem;
}

.mini-bar-track {
  flex: 1;
  height: 6px;
  background: var(--border);
  border-radius: 6px;
  overflow: hidden;
}

.mini-bar-fill {
  height: 100%;
  border-radius: 6px;
  transition: width .4s ease;
}

/* ---- Difficulty selector ---- */
.quiz-setup {
  max-width: 600px;
  margin: 3rem auto;
  background: var(--bg-card);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 2.5rem;
}

.quiz-setup h2 {
  font-size: 1.5rem;
  font-weight: 700;
  margin-bottom: .4rem;
}

.quiz-setup p.setup-desc {
  color: var(--text-muted);
  margin-bottom: 2rem;
}

.setup-option {
  display: flex;
  align-items: center;
  gap: 1rem;
  padding: 1rem 1.25rem;
  border: 1.5px solid var(--border);
  border-radius: 10px;
  cursor: pointer;
  margin-bottom: .75rem;
  transition: all var(--transition);
}

.setup-option:hover, .setup-option.selected {
  border-color: var(--primary);
  background: rgba(79,70,229,.08);
}

.setup-option input[type="radio"] { accent-color: var(--primary); }
.setup-option-label { font-weight: 600; }
.setup-option-sub  { font-size: .82rem; color: var(--text-muted); }

.setup-divider {
  display: flex;
  align-items: center;
  gap: 1rem;
  margin: 1.5rem 0;
  color: var(--text-muted);
  font-size: .85rem;
}
.setup-divider::before, .setup-divider::after {
  content: '';
  flex: 1;
  height: 1px;
  background: var(--border);
}

.question-count-row {
  display: flex;
  align-items: center;
  gap: 1rem;
  margin-bottom: 1.5rem;
}

.question-count-row label {
  font-size: .9rem;
  font-weight: 600;
  white-space: nowrap;
}

.question-count-row select {
  background: var(--bg-card2);
  color: var(--text);
  border: 1px solid var(--border);
  border-radius: 8px;
  padding: .4rem .8rem;
  font-size: .9rem;
}

/* ---- Toast Notifications ---- */
#toast-container {
  position: fixed;
  bottom: 1.5rem;
  right: 1.5rem;
  z-index: 1000;
  display: flex;
  flex-direction: column;
  gap: .6rem;
}

.toast {
  background: var(--bg-card);
  border: 1px solid var(--border);
  border-radius: 10px;
  padding: .8rem 1.2rem;
  font-size: .9rem;
  min-width: 260px;
  max-width: 360px;
  box-shadow: var(--shadow);
  animation: slideIn .25s ease;
  display: flex;
  align-items: center;
  gap: .6rem;
}

.toast.success { border-color: var(--success); }
.toast.danger  { border-color: var(--danger);  }
.toast.info    { border-color: var(--accent);  }

@keyframes slideIn {
  from { transform: translateX(110%); opacity: 0; }
  to   { transform: translateX(0);   opacity: 1; }
}

/* ---- Flashcard View ---- */
.flashcard-scene {
  perspective: 1000px;
  width: 100%;
  max-width: 680px;
  margin: 0 auto;
  height: 320px;
}

.flashcard {
  position: relative;
  width: 100%;
  height: 100%;
  transform-style: preserve-3d;
  transition: transform .55s ease;
  cursor: pointer;
}

.flashcard.flipped { transform: rotateY(180deg); }

.flashcard-face {
  position: absolute;
  inset: 0;
  background: var(--bg-card);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 2.5rem;
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  text-align: center;
  backface-visibility: hidden;
  -webkit-backface-visibility: hidden;
}

.flashcard-face.back {
  transform: rotateY(180deg);
  background: var(--bg-card2);
}

.flashcard-label {
  font-size: .75rem;
  text-transform: uppercase;
  letter-spacing: .1em;
  color: var(--text-muted);
  margin-bottom: .75rem;
}

.flashcard-text {
  font-size: 1.15rem;
  font-weight: 600;
  line-height: 1.55;
}

.flashcard-hint {
  margin-top: 1.5rem;
  font-size: .8rem;
  color: var(--text-muted);
}

.flashcard-nav {
  display: flex;
  align-items: center;
  justify-content: center;
  gap: 1rem;
  margin-top: 2rem;
}

.flashcard-counter {
  font-size: .9rem;
  color: var(--text-muted);
}

/* ---- Search ---- */
.search-bar {
  position: relative;
  max-width: 440px;
}

.search-bar input {
  width: 100%;
  background: var(--bg-card2);
  border: 1px solid var(--border);
  color: var(--text);
  border-radius: 10px;
  padding: .6rem 1rem .6rem 2.75rem;
  font-size: .95rem;
  outline: none;
  transition: border-color var(--transition);
}

.search-bar input:focus { border-color: var(--primary); }

.search-bar .search-icon {
  position: absolute;
  left: .9rem;
  top: 50%;
  transform: translateY(-50%);
  color: var(--text-muted);
  font-size: 1rem;
}

/* ---- Footer ---- */
footer {
  background: var(--bg-card);
  border-top: 1px solid var(--border);
  padding: 2rem 0;
  text-align: center;
  color: var(--text-muted);
  font-size: .85rem;
  margin-top: 4rem;
}

footer a { color: var(--text-muted); }
footer a:hover { color: var(--text); }

/* ---- Responsive ---- */
@media (max-width: 640px) {
  .hero { padding: 3rem 0 2.5rem; }
  .hero-stats { gap: 1.5rem; }
  .quiz-header { flex-direction: column; align-items: flex-start; }
  .results-card { margin: 1.5rem; padding: 1.5rem; }
  .flashcard-scene { height: 260px; }
  .flashcard-face { padding: 1.5rem; }
  .topics-grid { grid-template-columns: 1fr 1fr; }
  .nav-brand span:not(.logo) { display: none; }
}

@media (max-width: 420px) {
  .topics-grid { grid-template-columns: 1fr; }
}

/* ---- Animations ---- */
@keyframes fadeIn {
  from { opacity: 0; transform: translateY(12px); }
  to   { opacity: 1; transform: translateY(0); }
}

.animate-in {
  animation: fadeIn .35s ease both;
}

/* ---- Scrollbar ---- */
::-webkit-scrollbar { width: 7px; }
::-webkit-scrollbar-track { background: var(--bg); }
::-webkit-scrollbar-thumb { background: var(--border); border-radius: 4px; }
::-webkit-scrollbar-thumb:hover { background: var(--text-muted); }