/* ============================================
   QUIZ APP - STYLE CHUNG
   Màu chủ đạo: Đỏ/Vàng - Màu cờ Việt Nam
   ============================================ */

:root {
  --red: #C8102E;
  --red-dark: #9B0D22;
  --red-light: #E8294A;
  --yellow: #F5C518;
  --yellow-dark: #D4A90D;
  --yellow-light: #FDD835;
  --white: #FFFFFF;
  --gray-50: #FAFAFA;
  --gray-100: #F5F5F5;
  --gray-200: #EEEEEE;
  --gray-300: #E0E0E0;
  --gray-400: #BDBDBD;
  --gray-500: #9E9E9E;
  --gray-600: #757575;
  --gray-700: #616161;
  --gray-800: #424242;
  --gray-900: #212121;
  --success: #2E7D32;
  --success-light: #E8F5E9;
  --error: #C62828;
  --error-light: #FFEBEE;
  --shadow-sm: 0 1px 3px rgba(0,0,0,0.12), 0 1px 2px rgba(0,0,0,0.08);
  --shadow-md: 0 4px 6px rgba(0,0,0,0.1), 0 2px 4px rgba(0,0,0,0.06);
  --shadow-lg: 0 10px 25px rgba(0,0,0,0.15), 0 4px 10px rgba(0,0,0,0.1);
  --shadow-xl: 0 20px 40px rgba(0,0,0,0.2);
  --radius-sm: 6px;
  --radius-md: 10px;
  --radius-lg: 16px;
  --radius-xl: 24px;
  --transition: all 0.2s ease;
}

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

html {
  scroll-behavior: smooth;
}

body {
  font-family: 'Segoe UI', 'Helvetica Neue', Arial, sans-serif;
  background: linear-gradient(135deg, #fff5f5 0%, #fffde7 50%, #fff5f5 100%);
  min-height: 100vh;
  color: var(--gray-900);
  line-height: 1.6;
}

/* ===== NAVIGATION ===== */
.navbar {
  background: linear-gradient(135deg, var(--red) 0%, var(--red-dark) 100%);
  padding: 0;
  box-shadow: var(--shadow-lg);
  position: sticky;
  top: 0;
  z-index: 1000;
}

.nav-container {
  max-width: 1100px;
  margin: 0 auto;
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: 0 16px;
}

.nav-brand {
  display: flex;
  align-items: center;
  gap: 10px;
  padding: 12px 0;
  text-decoration: none;
  color: var(--white);
}

.nav-brand .star {
  color: var(--yellow);
  font-size: 22px;
  filter: drop-shadow(0 0 4px rgba(245,197,24,0.6));
}

.nav-brand span {
  font-size: 17px;
  font-weight: 700;
  letter-spacing: 0.3px;
}

.nav-menu {
  display: flex;
  list-style: none;
  gap: 2px;
}

.nav-menu a {
  display: flex;
  align-items: center;
  gap: 6px;
  padding: 14px 16px;
  color: rgba(255,255,255,0.85);
  text-decoration: none;
  font-size: 14px;
  font-weight: 500;
  transition: var(--transition);
  border-bottom: 3px solid transparent;
}

.nav-menu a:hover,
.nav-menu a.active {
  color: var(--yellow);
  border-bottom-color: var(--yellow);
  background: rgba(255,255,255,0.08);
}

.nav-toggle {
  display: none;
  background: none;
  border: none;
  color: white;
  font-size: 22px;
  cursor: pointer;
  padding: 8px;
}

/* ===== HERO / HEADER ===== */
.page-hero {
  background: linear-gradient(135deg, var(--red) 0%, var(--red-dark) 60%, #6B0D1A 100%);
  color: white;
  padding: 40px 16px;
  text-align: center;
  position: relative;
  overflow: hidden;
}

.page-hero::before {
  content: '⭐';
  position: absolute;
  font-size: 200px;
  opacity: 0.04;
  top: -30px;
  left: -30px;
}

.page-hero::after {
  content: '⭐';
  position: absolute;
  font-size: 150px;
  opacity: 0.04;
  bottom: -20px;
  right: -20px;
}

.page-hero h1 {
  font-size: clamp(22px, 4vw, 34px);
  font-weight: 800;
  margin-bottom: 8px;
  text-shadow: 0 2px 4px rgba(0,0,0,0.3);
}

.page-hero p {
  font-size: 15px;
  opacity: 0.9;
  max-width: 600px;
  margin: 0 auto;
}

.hero-badge {
  display: inline-block;
  background: var(--yellow);
  color: var(--red-dark);
  padding: 4px 14px;
  border-radius: 20px;
  font-size: 12px;
  font-weight: 700;
  text-transform: uppercase;
  letter-spacing: 1px;
  margin-bottom: 12px;
}

/* ===== MAIN CONTAINER ===== */
.container {
  max-width: 860px;
  margin: 0 auto;
  padding: 30px 16px 60px;
}

.container-wide {
  max-width: 1100px;
  margin: 0 auto;
  padding: 30px 16px 60px;
}

/* ===== CARD ===== */
.card {
  background: white;
  border-radius: var(--radius-lg);
  box-shadow: var(--shadow-md);
  padding: 28px;
  margin-bottom: 20px;
  border: 1px solid var(--gray-200);
}

.card-title {
  font-size: 18px;
  font-weight: 700;
  color: var(--red-dark);
  margin-bottom: 18px;
  padding-bottom: 12px;
  border-bottom: 2px solid var(--yellow);
  display: flex;
  align-items: center;
  gap: 8px;
}

/* ===== BUTTONS ===== */
.btn {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: 7px;
  padding: 10px 22px;
  border: none;
  border-radius: var(--radius-md);
  font-size: 14px;
  font-weight: 600;
  cursor: pointer;
  transition: var(--transition);
  text-decoration: none;
  white-space: nowrap;
}

.btn:hover {
  transform: translateY(-1px);
}

.btn:active {
  transform: translateY(0);
}

.btn-primary {
  background: linear-gradient(135deg, var(--red), var(--red-dark));
  color: white;
  box-shadow: 0 4px 12px rgba(200,16,46,0.35);
}

.btn-primary:hover {
  background: linear-gradient(135deg, var(--red-light), var(--red));
  box-shadow: 0 6px 16px rgba(200,16,46,0.45);
}

.btn-yellow {
  background: linear-gradient(135deg, var(--yellow), var(--yellow-dark));
  color: var(--red-dark);
  box-shadow: 0 4px 12px rgba(245,197,24,0.4);
}

.btn-yellow:hover {
  background: linear-gradient(135deg, var(--yellow-light), var(--yellow));
  box-shadow: 0 6px 16px rgba(245,197,24,0.5);
}

.btn-outline {
  background: transparent;
  color: var(--red);
  border: 2px solid var(--red);
}

.btn-outline:hover {
  background: var(--red);
  color: white;
}

.btn-gray {
  background: var(--gray-200);
  color: var(--gray-700);
}

.btn-gray:hover {
  background: var(--gray-300);
}

.btn-danger {
  background: linear-gradient(135deg, #f44336, #c62828);
  color: white;
  box-shadow: 0 4px 12px rgba(244,67,54,0.35);
}

.btn-danger:hover {
  box-shadow: 0 6px 16px rgba(244,67,54,0.45);
}

.btn-success {
  background: linear-gradient(135deg, #43a047, #2e7d32);
  color: white;
  box-shadow: 0 4px 12px rgba(67,160,71,0.35);
}

.btn-lg {
  padding: 14px 32px;
  font-size: 16px;
  border-radius: var(--radius-lg);
}

.btn-sm {
  padding: 6px 14px;
  font-size: 13px;
  border-radius: var(--radius-sm);
}

.btn-block {
  width: 100%;
}

/* ===== FORM ===== */
.form-group {
  margin-bottom: 18px;
}

.form-label {
  display: block;
  font-size: 13px;
  font-weight: 600;
  color: var(--gray-700);
  margin-bottom: 6px;
  text-transform: uppercase;
  letter-spacing: 0.5px;
}

.form-control {
  width: 100%;
  padding: 11px 14px;
  border: 2px solid var(--gray-300);
  border-radius: var(--radius-md);
  font-size: 15px;
  color: var(--gray-900);
  background: var(--gray-50);
  transition: var(--transition);
  font-family: inherit;
}

.form-control:focus {
  outline: none;
  border-color: var(--red);
  background: white;
  box-shadow: 0 0 0 3px rgba(200,16,46,0.1);
}

textarea.form-control {
  resize: vertical;
  min-height: 80px;
}

select.form-control {
  cursor: pointer;
}

/* ===== ALERT / BADGE ===== */
.badge {
  display: inline-block;
  padding: 3px 10px;
  border-radius: 20px;
  font-size: 12px;
  font-weight: 700;
}

.badge-red { background: var(--error-light); color: var(--error); }
.badge-yellow { background: #FFF9C4; color: #827717; }
.badge-green { background: var(--success-light); color: var(--success); }
.badge-gray { background: var(--gray-200); color: var(--gray-700); }

.alert {
  padding: 14px 18px;
  border-radius: var(--radius-md);
  margin-bottom: 16px;
  font-size: 14px;
  border-left: 4px solid;
}

.alert-success {
  background: var(--success-light);
  border-color: var(--success);
  color: var(--success);
}

.alert-error {
  background: var(--error-light);
  border-color: var(--error);
  color: var(--error);
}

.alert-warning {
  background: #FFF9C4;
  border-color: var(--yellow-dark);
  color: #6D4C00;
}

/* ===== DIVIDER ===== */
.divider {
  border: none;
  border-top: 2px solid var(--gray-200);
  margin: 20px 0;
}

/* ===== LOADING ===== */
.spinner {
  display: inline-block;
  width: 20px;
  height: 20px;
  border: 3px solid rgba(255,255,255,0.3);
  border-top-color: white;
  border-radius: 50%;
  animation: spin 0.8s linear infinite;
}

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

/* ===== MODAL ===== */
.modal-overlay {
  display: none;
  position: fixed;
  inset: 0;
  background: rgba(0,0,0,0.6);
  z-index: 2000;
  align-items: center;
  justify-content: center;
  padding: 16px;
}

.modal-overlay.active {
  display: flex;
}

.modal {
  background: white;
  border-radius: var(--radius-xl);
  padding: 32px;
  max-width: 440px;
  width: 100%;
  box-shadow: var(--shadow-xl);
  animation: modalIn 0.25s ease;
}

@keyframes modalIn {
  from { transform: scale(0.9); opacity: 0; }
  to { transform: scale(1); opacity: 1; }
}

.modal h3 {
  font-size: 20px;
  font-weight: 700;
  color: var(--red-dark);
  margin-bottom: 12px;
}

.modal p {
  color: var(--gray-600);
  margin-bottom: 22px;
  font-size: 15px;
}

.modal-actions {
  display: flex;
  gap: 10px;
  justify-content: flex-end;
}

/* ===== TOOLTIP ===== */
.tooltip {
  position: relative;
}

/* ===== PROGRESS ===== */
.progress-bar-wrap {
  background: var(--gray-200);
  border-radius: 99px;
  height: 8px;
  overflow: hidden;
}

.progress-bar {
  background: linear-gradient(90deg, var(--red), var(--yellow));
  height: 100%;
  border-radius: 99px;
  transition: width 0.4s ease;
}

/* ===== FOOTER ===== */
.footer {
  background: var(--red-dark);
  color: rgba(255,255,255,0.7);
  text-align: center;
  padding: 20px 16px;
  font-size: 13px;
  margin-top: auto;
}

.footer span {
  color: var(--yellow);
}

/* ===== RESPONSIVE ===== */
@media (max-width: 640px) {
  .nav-menu {
    display: none;
    flex-direction: column;
    position: absolute;
    top: 100%;
    left: 0;
    right: 0;
    background: var(--red-dark);
    padding: 8px 0;
    box-shadow: var(--shadow-lg);
  }
  
  .nav-menu.open {
    display: flex;
  }
  
  .nav-menu a {
    padding: 12px 20px;
    border-bottom: none;
    border-left: 3px solid transparent;
  }
  
  .nav-menu a:hover,
  .nav-menu a.active {
    border-left-color: var(--yellow);
    border-bottom-color: transparent;
  }
  
  .nav-toggle {
    display: block;
  }
  
  .nav-container {
    flex-wrap: wrap;
    position: relative;
  }
  
  .card {
    padding: 18px;
  }
  
  .modal {
    padding: 22px;
  }
}

/* ===== ANIMATIONS ===== */
@keyframes fadeIn {
  from { opacity: 0; transform: translateY(10px); }
  to { opacity: 1; transform: translateY(0); }
}

@keyframes slideIn {
  from { opacity: 0; transform: translateX(-20px); }
  to { opacity: 1; transform: translateX(0); }
}

@keyframes pulse {
  0%, 100% { transform: scale(1); }
  50% { transform: scale(1.05); }
}

.animate-fade { animation: fadeIn 0.4s ease both; }
.animate-slide { animation: slideIn 0.3s ease both; }