:root {
  --primary: #2563eb;
  --primary-hover: #1d4ed8;
  --primary-light: #eff6ff;
  --success: #10b981;
  --warning: #f59e0b;
  --danger: #ef4444;
  --bg-main: #0f172a;
  --bg-card: #1e293b;
  --bg-card-hover: #334155;
  --text-main: #f8fafc;
  --text-muted: #94a3b8;
  --border: rgba(255, 255, 255, 0.1);
  --font-family: system-ui, -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, Oxygen, Ubuntu, Cantarell, sans-serif;
}

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

body {
  font-family: var(--font-family);
  background: var(--bg-main);
  color: var(--text-main);
  min-height: 100vh;
  display: flex;
  flex-direction: column;
}

/* NAVBAR */
.portal-navbar {
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: 14px 28px;
  background: rgba(15, 23, 42, 0.85);
  backdrop-filter: blur(12px);
  border-bottom: 1px solid var(--border);
  position: sticky;
  top: 0;
  z-index: 50;
}

.portal-brand {
  display: flex;
  align-items: center;
  gap: 12px;
  text-decoration: none;
  color: var(--text-main);
  font-size: 1.15rem;
  font-weight: 800;
  letter-spacing: -0.3px;
}

.portal-brand-icon {
  width: 38px;
  height: 38px;
  background: linear-gradient(135deg, #38bdf8, #2563eb);
  border-radius: 10px;
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: 1.25rem;
}

.portal-nav-links {
  display: flex;
  align-items: center;
  gap: 16px;
}

.portal-nav-btn {
  display: inline-flex;
  align-items: center;
  gap: 6px;
  padding: 8px 16px;
  border-radius: 8px;
  font-size: 0.9rem;
  font-weight: 600;
  text-decoration: none;
  transition: all 0.2s ease;
  border: 1px solid transparent;
}

.portal-nav-btn.btn-outline {
  color: #cbd5e1;
  background: rgba(255, 255, 255, 0.05);
  border-color: var(--border);
}

.portal-nav-btn.btn-outline:hover {
  background: rgba(255, 255, 255, 0.12);
  color: #fff;
}

.portal-nav-btn.btn-primary {
  background: linear-gradient(135deg, #2563eb, #1d4ed8);
  color: white;
  box-shadow: 0 4px 12px rgba(37, 99, 235, 0.3);
}

.portal-nav-btn.btn-primary:hover {
  filter: brightness(1.1);
  transform: translateY(-1px);
}

/* CONTAINER */
.portal-container {
  max-width: 1200px;
  margin: 0 auto;
  padding: 32px 20px;
  flex: 1;
  width: 100%;
}

/* HOME HERO & CARDS */
.home-hero {
  text-align: center;
  margin-bottom: 40px;
}

.home-badge {
  display: inline-block;
  padding: 4px 14px;
  border-radius: 9999px;
  background: rgba(56, 189, 248, 0.15);
  color: #38bdf8;
  font-size: 0.85rem;
  font-weight: 700;
  margin-bottom: 12px;
  border: 1px solid rgba(56, 189, 248, 0.3);
}

.home-title {
  font-size: 2.25rem;
  font-weight: 900;
  letter-spacing: -0.5px;
  margin-bottom: 10px;
  background: linear-gradient(135deg, #f8fafc 40%, #94a3b8 100%);
  -webkit-background-clip: text;
  -webkit-text-fill-color: transparent;
}

.home-subtitle {
  color: var(--text-muted);
  font-size: 1.05rem;
  max-width: 650px;
  margin: 0 auto;
}

.home-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(320px, 1fr));
  gap: 24px;
  margin-top: 30px;
}

.feature-card {
  background: var(--bg-card);
  border: 1px solid var(--border);
  border-radius: 16px;
  padding: 30px;
  display: flex;
  flex-direction: column;
  justify-content: space-between;
  transition: all 0.25s ease;
  position: relative;
  overflow: hidden;
}

.feature-card:hover {
  transform: translateY(-4px);
  border-color: rgba(56, 189, 248, 0.4);
  box-shadow: 0 12px 30px rgba(0, 0, 0, 0.4);
}

.card-icon {
  font-size: 2.5rem;
  margin-bottom: 18px;
}

.card-title {
  font-size: 1.35rem;
  font-weight: 800;
  margin-bottom: 10px;
  color: #f8fafc;
}

.card-desc {
  color: var(--text-muted);
  font-size: 0.95rem;
  line-height: 1.5;
  margin-bottom: 24px;
}

.card-features {
  list-style: none;
  margin-bottom: 24px;
  display: flex;
  flex-direction: column;
  gap: 8px;
}

.card-features li {
  display: flex;
  align-items: center;
  gap: 8px;
  font-size: 0.88rem;
  color: #cbd5e1;
}

.card-features li::before {
  content: "✔";
  color: #10b981;
  font-weight: bold;
}

.btn-card-action {
  display: flex;
  align-items: center;
  justify-content: center;
  gap: 8px;
  padding: 12px 20px;
  border-radius: 10px;
  font-weight: 700;
  text-decoration: none;
  transition: all 0.2s ease;
}

/* HOST QR SCREEN (MÁY CHIẾU) */
.qr-layout {
  display: grid;
  grid-template-columns: 440px 1fr;
  gap: 28px;
  align-items: start;
}

@media (max-width: 900px) {
  .qr-layout {
    grid-template-columns: 1fr;
  }
}

.qr-box-card {
  background: var(--bg-card);
  border: 1px solid var(--border);
  border-radius: 20px;
  padding: 28px;
  text-align: center;
  box-shadow: 0 10px 30px rgba(0, 0, 0, 0.3);
}

.qr-timer-pill {
  display: inline-flex;
  align-items: center;
  gap: 8px;
  padding: 6px 16px;
  border-radius: 9999px;
  background: rgba(245, 158, 11, 0.15);
  color: #fbbf24;
  font-size: 1.15rem;
  font-weight: 800;
  font-family: ui-monospace, SFMono-Regular, monospace;
  margin-bottom: 18px;
  border: 1px solid rgba(245, 158, 11, 0.3);
}

.qr-timer-pill.expired {
  background: rgba(239, 68, 68, 0.15);
  color: #f87171;
  border-color: rgba(239, 68, 68, 0.3);
}

.qr-canvas-wrap {
  background: #ffffff;
  padding: 16px;
  border-radius: 14px;
  display: inline-block;
  margin: 10px 0 18px 0;
  box-shadow: 0 4px 16px rgba(0, 0, 0, 0.2);
}

.qr-link-text {
  font-size: 0.8rem;
  word-break: break-all;
  color: #94a3b8;
  background: rgba(15, 23, 42, 0.6);
  padding: 8px 12px;
  border-radius: 8px;
  margin-bottom: 18px;
  user-select: all;
}

.btn-new-session {
  background: linear-gradient(135deg, #10b981, #059669);
  color: white;
  border: none;
  padding: 12px 24px;
  border-radius: 10px;
  font-size: 0.95rem;
  font-weight: 700;
  cursor: pointer;
  transition: all 0.2s ease;
  width: 100%;
}

.btn-new-session:hover {
  filter: brightness(1.1);
  transform: translateY(-1px);
}

/* SUBMISSIONS TABLE */
.subs-card {
  background: var(--bg-card);
  border: 1px solid var(--border);
  border-radius: 20px;
  padding: 24px;
}

.subs-header {
  display: flex;
  align-items: center;
  justify-content: space-between;
  margin-bottom: 16px;
  padding-bottom: 12px;
  border-bottom: 1px solid var(--border);
}

.subs-title {
  font-size: 1.2rem;
  font-weight: 800;
  display: flex;
  align-items: center;
  gap: 10px;
}

.subs-count-badge {
  background: #2563eb;
  color: #fff;
  padding: 3px 10px;
  border-radius: 9999px;
  font-size: 0.85rem;
}

.subs-table {
  width: 100%;
  border-collapse: collapse;
  font-size: 0.92rem;
}

.subs-table th {
  text-align: left;
  padding: 10px 12px;
  color: #94a3b8;
  font-weight: 700;
  border-bottom: 1px solid var(--border);
  font-size: 0.82rem;
  text-transform: uppercase;
  letter-spacing: 0.5px;
}

.subs-table td {
  padding: 12px;
  border-bottom: 1px solid rgba(255, 255, 255, 0.05);
}

.subs-table tr:hover td {
  background: rgba(255, 255, 255, 0.02);
}

.score-badge {
  display: inline-block;
  padding: 3px 8px;
  border-radius: 6px;
  font-weight: 800;
  font-size: 0.85rem;
}

.score-high {
  background: rgba(16, 185, 129, 0.2);
  color: #34d399;
}

.score-med {
  background: rgba(245, 158, 11, 0.2);
  color: #fbbf24;
}

.score-low {
  background: rgba(239, 68, 68, 0.2);
  color: #f87171;
}

/* STUDENT QUIZ PAGE (MOBILE-OPTIMIZED) */
.quiz-container {
  max-width: 680px;
  margin: 0 auto;
  padding: 20px 16px;
}

.quiz-card {
  background: var(--bg-card);
  border: 1px solid var(--border);
  border-radius: 16px;
  padding: 24px;
  margin-bottom: 20px;
  box-shadow: 0 8px 24px rgba(0, 0, 0, 0.25);
}

.form-group {
  margin-bottom: 16px;
}

.form-label {
  display: block;
  font-size: 0.88rem;
  font-weight: 700;
  color: #cbd5e1;
  margin-bottom: 6px;
}

.form-input {
  width: 100%;
  background: #0f172a;
  border: 1.5px solid rgba(255, 255, 255, 0.2);
  border-radius: 10px;
  padding: 12px 16px;
  color: #f8fafc;
  font-size: 1rem;
  font-family: inherit;
  outline: none;
  transition: border-color 0.2s ease;
}

.form-input:focus {
  border-color: #38bdf8;
  box-shadow: 0 0 0 3px rgba(56, 189, 248, 0.2);
}

.question-block {
  margin-bottom: 24px;
  padding-bottom: 20px;
  border-bottom: 1px solid rgba(255, 255, 255, 0.08);
}

.question-block:last-child {
  border-bottom: none;
  margin-bottom: 0;
  padding-bottom: 0;
}

.question-title {
  font-size: 1rem;
  font-weight: 700;
  color: #f8fafc;
  margin-bottom: 12px;
  line-height: 1.45;
}

.option-item {
  display: flex;
  align-items: flex-start;
  gap: 12px;
  padding: 10px 14px;
  border-radius: 8px;
  border: 1px solid rgba(255, 255, 255, 0.1);
  background: rgba(15, 23, 42, 0.5);
  margin-bottom: 8px;
  cursor: pointer;
  transition: all 0.15s ease;
}

.option-item:hover {
  background: rgba(255, 255, 255, 0.08);
  border-color: rgba(56, 189, 248, 0.4);
}

.option-item input[type="radio"] {
  margin-top: 3px;
  accent-color: #2563eb;
  transform: scale(1.15);
}

.option-text {
  font-size: 0.92rem;
  color: #cbd5e1;
  line-height: 1.4;
}

.btn-submit-quiz {
  width: 100%;
  background: linear-gradient(135deg, #2563eb, #1d4ed8);
  color: white;
  border: none;
  padding: 15px;
  border-radius: 12px;
  font-size: 1.05rem;
  font-weight: 800;
  cursor: pointer;
  box-shadow: 0 4px 16px rgba(37, 99, 235, 0.4);
  transition: all 0.2s ease;
}

.btn-submit-quiz:hover {
  filter: brightness(1.1);
  transform: translateY(-2px);
}

.btn-submit-quiz:disabled {
  opacity: 0.5;
  cursor: not-allowed;
  transform: none;
}

.alert-box {
  padding: 16px;
  border-radius: 10px;
  font-size: 0.95rem;
  margin-bottom: 16px;
  display: flex;
  align-items: center;
  gap: 10px;
}

.alert-danger {
  background: rgba(239, 68, 68, 0.15);
  border: 1px solid rgba(239, 68, 68, 0.3);
  color: #fca5a5;
}

.alert-success {
  background: rgba(16, 185, 129, 0.15);
  border: 1px solid rgba(16, 185, 129, 0.3);
  color: #6ee7b7;
}