/* ========== BIẾN MÀU CHỦ ĐẠO ========== */
:root {
  --c-red: #b71c1c;
  --c-red-dark: #7f0000;
  --c-red-light: #f05545;
  --c-yellow: #ffc107;
  --c-yellow-dark: #c79100;
  --c-cream: #fff8e1;
  --c-dark: #1a1a1a;
  --c-gray: #666;
  --c-light: #f5f5f5;
  --c-white: #ffffff;
  --shadow-sm: 0 2px 8px rgba(0,0,0,.08);
  --shadow-md: 0 4px 16px rgba(0,0,0,.12);
  --shadow-lg: 0 8px 32px rgba(0,0,0,.16);
}

* { box-sizing: border-box; }
html, body {
  font-family: 'Be Vietnam Pro', system-ui, -apple-system, sans-serif;
  color: var(--c-dark);
  background: #fafafa;
  line-height: 1.6;
  margin: 0;
}

a { color: var(--c-red); text-decoration: none; transition: color .2s; }
a:hover { color: var(--c-red-dark); }

/* ========== HEADER ========== */
.site-header { box-shadow: var(--shadow-sm); position: sticky; top: 0; z-index: 1020; background: #fff; }
.topbar {
  background: linear-gradient(90deg, var(--c-red-dark), var(--c-red));
  color: #fff; font-size: .85rem; padding: .35rem 0;
}
.topbar a { color: var(--c-yellow); margin-left: 1rem; }
.topbar a:hover { color: #fff; }
.topbar-right { display: flex; gap: .25rem; align-items: center; }

.main-nav { padding: .75rem 0; background: #fff; border-bottom: 3px solid var(--c-yellow); }
.navbar-brand { display: flex; align-items: center; gap: .75rem; }
.navbar-brand img { height: 56px; }
.brand-text { display: flex; flex-direction: column; line-height: 1.15; }
.brand-text strong { color: var(--c-red); font-size: 1.05rem; font-weight: 800; }
.brand-text span { color: var(--c-gray); font-size: .78rem; }
.main-nav .nav-link {
  color: var(--c-dark); font-weight: 600; padding: .5rem 1rem !important; border-radius: 6px;
}
.main-nav .nav-link:hover { background: var(--c-cream); color: var(--c-red); }
.main-nav .nav-link.btn-exam {
  background: var(--c-yellow); color: var(--c-red-dark) !important; font-weight: 700;
}
.main-nav .nav-link.btn-exam:hover { background: var(--c-yellow-dark); color: #fff !important; }

/* ========== HERO ========== */
.hero {
  padding: 50px 0 70px !important;
  background:
    linear-gradient(135deg, rgba(74,0,8,0.7) 0%, rgba(139,10,31,0.80) 50%, rgba(90,6,19,0.85) 100%),
    url('../uploads/banners/nen-bn.jpg') center center / cover no-repeat !important;
  border-bottom: 6px double var(--c-yellow);
  position: relative;
}
.hero::before {
  content: ""; position: absolute; inset: 0;
  background: url("data:image/svg+xml,%3Csvg xmlns='http://www.w3.org/2000/svg' viewBox='0 0 100 100'%3E%3Cpath d='M50 5L60 35L90 35L65 55L75 85L50 65L25 85L35 55L10 35L40 35Z' fill='%23ffc107' opacity='.05'/%3E%3C/svg%3E") repeat;
  background-size: 120px; opacity: .4;
}
.hero .container { position: relative; z-index: 1; }
.hero h1 { font-weight: 800; font-size: clamp(1.8rem, 4vw, 3rem); color: var(--c-yellow); text-shadow: 0 2px 8px rgba(0,0,0,.3); }
.hero p.lead { font-size: 1.2rem; max-width: 800px; }
.hero .badge-50 {
  background: var(--c-yellow); color: var(--c-red-dark);
  padding: .5rem 1.5rem; font-weight: 700; font-size: 1.1rem; border-radius: 50px;
  display: inline-block; margin-bottom: 1rem;
}
.hero-actions { display: flex; gap: 1rem; flex-wrap: wrap; margin-top: 1.5rem; }
.hero-actions .btn { padding: .75rem 2rem; font-weight: 700; }

/* ========== BUTTONS ========== */
.btn-primary, .btn-danger {
  background: var(--c-red); border-color: var(--c-red);
}
.btn-primary:hover, .btn-danger:hover {
  background: var(--c-red-dark); border-color: var(--c-red-dark);
}
.btn-warning { background: var(--c-yellow); border-color: var(--c-yellow); color: var(--c-red-dark); font-weight: 700; }
.btn-warning:hover { background: var(--c-yellow-dark); border-color: var(--c-yellow-dark); }
.btn-outline-warning { color: var(--c-yellow); border-color: var(--c-yellow); }
.btn-outline-warning:hover { background: var(--c-yellow); color: var(--c-red-dark); }

/* ========== SECTIONS ========== */
.site-main { min-height: 60vh; }
.section { padding: 3rem 0; }
.section-title {
  font-weight: 800; color: var(--c-red); text-align: center; margin-bottom: 0.5rem;
  text-transform: uppercase; font-size: 1.6rem;
}
.section-title::after {
  content: ""; display: block; width: 60px; height: 4px;
  background: var(--c-yellow); margin: .75rem auto 0; border-radius: 2px;
}
.section-subtitle { text-align: center; color: var(--c-gray); margin-bottom: 2.5rem; }

/* ========== CARDS ========== */
.card { border: none; border-radius: 12px; box-shadow: var(--shadow-sm); transition: all .2s; }
.card:hover { box-shadow: var(--shadow-md); transform: translateY(-2px); }
.card-img-top { border-radius: 12px 12px 0 0; }
.card-feature { padding: 2rem 1.5rem; text-align: center; }
.card-feature .icon {
  width: 70px; height: 70px; border-radius: 50%;
  background: linear-gradient(135deg, var(--c-red), var(--c-red-light));
  color: var(--c-yellow); display: flex; align-items: center; justify-content: center;
  font-size: 1.8rem; margin: 0 auto 1rem;
}
.card-feature h5 { color: var(--c-red); font-weight: 700; }

.news-card .card-body h6 { color: var(--c-red); font-weight: 700; }
.news-card .meta { color: var(--c-gray); font-size: .85rem; }

/* ========== STATS ========== */
.stats-row { background: var(--c-cream); padding: 2.5rem 0; }
.stat-item { text-align: center; padding: 1rem; }
.stat-item .num {
  font-size: 2.5rem; font-weight: 800; color: var(--c-red);
  line-height: 1; display: block;
}
.stat-item .label { color: var(--c-dark); font-weight: 600; margin-top: .5rem; }

/* ========== FORMS ========== */
.form-control, .form-select { padding: .65rem 1rem; border-radius: 8px; }
.form-control:focus, .form-select:focus {
  border-color: var(--c-yellow); box-shadow: 0 0 0 .2rem rgba(255,193,7,.2);
}
.form-label { font-weight: 600; margin-bottom: .35rem; }
.required { color: var(--c-red); }

.auth-card {
  max-width: 480px; margin: 3rem auto; padding: 2.5rem;
  background: #fff; border-radius: 16px; box-shadow: var(--shadow-md);
}
.auth-card h2 { color: var(--c-red); font-weight: 800; text-align: center; margin-bottom: .25rem; }
.auth-card .subtitle { text-align: center; color: var(--c-gray); margin-bottom: 2rem; }

/* ========== EXAM ========== */
.exam-wrapper { display: grid; grid-template-columns: 1fr 280px; gap: 1.5rem; }
@media (max-width: 992px) { .exam-wrapper { grid-template-columns: 1fr; } }

.exam-main { background: #fff; border-radius: 12px; padding: 2rem; box-shadow: var(--shadow-sm); }
.exam-sidebar { background: #fff; border-radius: 12px; padding: 1.25rem; box-shadow: var(--shadow-sm); position: sticky; top: 100px; max-height: calc(100vh - 120px); overflow-y: auto; }

.timer {
  background: linear-gradient(135deg, var(--c-red), var(--c-red-dark));
  color: var(--c-yellow); padding: 1rem; border-radius: 10px; text-align: center;
  font-size: 1.75rem; font-weight: 800; font-family: 'Courier New', monospace;
  letter-spacing: 2px; margin-bottom: 1rem;
}
.timer.warning { background: linear-gradient(135deg, #ff5722, #d84315); animation: pulse 1s infinite; }
@keyframes pulse { 0%, 100% { transform: scale(1); } 50% { transform: scale(1.02); } }

.question-grid { display: grid; grid-template-columns: repeat(5, 1fr); gap: 6px; margin-bottom: 1rem; }
.q-btn {
  aspect-ratio: 1; border: 2px solid #ddd; background: #fff; border-radius: 6px;
  font-weight: 700; cursor: pointer; transition: all .15s; padding: 0;
}
.q-btn:hover { border-color: var(--c-red); }
.q-btn.answered { background: var(--c-yellow); border-color: var(--c-yellow-dark); color: var(--c-red-dark); }
.q-btn.current { background: var(--c-red); border-color: var(--c-red-dark); color: #fff; }

.question-block { padding: 1rem 0; }
.question-num { color: var(--c-red); font-weight: 700; font-size: 1.1rem; }
.question-text { font-size: 1.15rem; font-weight: 600; margin: .75rem 0 1.25rem; line-height: 1.5; }
.option {
  display: flex; align-items: flex-start; gap: .75rem;
  padding: .9rem 1.1rem; border: 2px solid #e0e0e0; border-radius: 10px;
  margin-bottom: .65rem; cursor: pointer; transition: all .15s;
}
.option:hover { border-color: var(--c-yellow); background: var(--c-cream); }
.option input { margin-top: .3rem; accent-color: var(--c-red); }
.option.selected { border-color: var(--c-red); background: #fff5f5; }
.option-letter { font-weight: 800; color: var(--c-red); width: 1.5rem; }
.option.correct { border-color: #2e7d32; background: #e8f5e9; }
.option.wrong { border-color: #c62828; background: #ffebee; }

.exam-nav { display: flex; justify-content: space-between; margin-top: 1.5rem; }

/* ========== RESULT ========== */
.score-card {
  background: linear-gradient(135deg, var(--c-red-dark), var(--c-red));
  color: #fff; padding: 2.5rem; border-radius: 16px; text-align: center; margin-bottom: 2rem;
}
.score-card .score {
  font-size: 4rem; font-weight: 800; color: var(--c-yellow); line-height: 1;
}
.score-card .label { font-size: 1.1rem; opacity: .9; }
.score-stats { display: grid; grid-template-columns: repeat(auto-fit, minmax(140px, 1fr)); gap: 1rem; margin-top: 1.5rem; }
.score-stats .stat { background: rgba(255,255,255,.1); padding: .8rem; border-radius: 8px; }
.score-stats .stat .v { font-size: 1.5rem; font-weight: 800; color: var(--c-yellow); }

/* ========== LEADERBOARD ========== */
.leaderboard-table { background: #fff; border-radius: 12px; overflow: hidden; box-shadow: var(--shadow-sm); }
.leaderboard-table thead { background: var(--c-red); color: #fff; }
.leaderboard-table th { padding: 1rem; font-weight: 700; }
.leaderboard-table td { padding: .85rem 1rem; vertical-align: middle; }
.rank-badge {
  display: inline-flex; align-items: center; justify-content: center;
  width: 36px; height: 36px; border-radius: 50%; font-weight: 800; color: #fff;
  background: var(--c-gray);
}
.rank-badge.r1 { background: linear-gradient(135deg, #ffd700, #ff9800); }
.rank-badge.r2 { background: linear-gradient(135deg, #c0c0c0, #9e9e9e); }
.rank-badge.r3 { background: linear-gradient(135deg, #cd7f32, #8d6e63); }

/* ========== FOOTER ========== */
.site-footer {
  background: linear-gradient(135deg, var(--c-red-dark), #4a0000);
  color: #fff; padding: 3rem 0 1.5rem; margin-top: 4rem;
}
.site-footer h5 { color: var(--c-yellow); font-weight: 800; }
.site-footer h6 { color: var(--c-yellow); font-weight: 700; font-size: .95rem; letter-spacing: .5px; }
.site-footer a { color: rgba(255,255,255,.85); }
.site-footer a:hover { color: var(--c-yellow); }
.site-footer hr { border-color: rgba(255,255,255,.2); }

/* ========== ADMIN ========== */
.admin-layout { display: flex; min-height: 100vh; }
.admin-sidebar {
  width: 250px; background: linear-gradient(180deg, var(--c-red-dark), var(--c-red));
  color: #fff; padding: 1rem 0; flex-shrink: 0;
}
.admin-sidebar .logo { padding: 1rem 1.5rem 1.5rem; border-bottom: 1px solid rgba(255,255,255,.15); }
.admin-sidebar .logo strong { color: var(--c-yellow); display: block; }
.admin-sidebar .logo small { color: rgba(255,255,255,.8); }
.admin-sidebar nav a {
  display: flex; align-items: center; gap: .75rem;
  padding: .7rem 1.5rem; color: rgba(255,255,255,.85); font-weight: 500;
}
.admin-sidebar nav a:hover, .admin-sidebar nav a.active {
  background: rgba(255,193,7,.15); color: var(--c-yellow); border-left: 3px solid var(--c-yellow);
}
.admin-sidebar nav a i { width: 20px; text-align: center; }
.admin-content { flex: 1; padding: 1.5rem; background: #f5f5f5; }
.admin-topbar {
  background: #fff; padding: .75rem 1.5rem; border-radius: 8px;
  box-shadow: var(--shadow-sm); margin-bottom: 1.5rem;
  display: flex; justify-content: space-between; align-items: center;
}
.admin-card {
  background: #fff; border-radius: 8px; padding: 1.5rem;
  box-shadow: var(--shadow-sm); margin-bottom: 1.5rem;
}
.admin-card h3, .admin-card h4 { color: var(--c-red); font-weight: 700; }

.dash-stat {
  background: #fff; border-radius: 8px; padding: 1.25rem; box-shadow: var(--shadow-sm);
  border-left: 4px solid var(--c-red);
}
.dash-stat .num { font-size: 1.8rem; font-weight: 800; color: var(--c-red); }
.dash-stat .label { color: var(--c-gray); font-size: .9rem; }

@media (max-width: 768px) {
  .admin-sidebar { width: 60px; }
  .admin-sidebar nav a span, .admin-sidebar .logo { display: none; }
  .admin-sidebar nav a { justify-content: center; padding: .8rem; }
}

/* ========== UTILITIES ========== */
.table-responsive { background: #fff; border-radius: 8px; overflow: hidden; box-shadow: var(--shadow-sm); }
.badge-pending { background: var(--c-yellow); color: var(--c-red-dark); }
.badge-active { background: #2e7d32; color: #fff; }
.badge-locked { background: #c62828; color: #fff; }

.page-banner {
  background: linear-gradient(135deg, var(--c-red-dark), var(--c-red));
  color: #fff; padding: 2.5rem 0; text-align: center;
}
.page-banner h1 { color: var(--c-yellow); font-weight: 800; margin: 0; }
.page-banner .breadcrumb { justify-content: center; --bs-breadcrumb-divider-color: rgba(255,255,255,.6); }
.page-banner .breadcrumb a { color: #fff; }
.page-banner .breadcrumb-item.active { color: var(--c-yellow); }

.content-box { background: #fff; border-radius: 12px; padding: 2rem; box-shadow: var(--shadow-sm); }
.content-box h2, .content-box h3 { color: var(--c-red); }
.content-box img { max-width: 100%; height: auto; border-radius: 8px; }