/* ============================================
   BTVISA.NET - GIÁO DỤC NGỮ VĂN ONLINE
   Design based on: HOCMAI, vted, SuperKids
   ============================================ */

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

:root {
    --primary: #1a56db;
    --primary-dark: #1240a8;
    --primary-light: #e8f0fe;
    --accent: #f59e0b;
    --accent-dark: #d97706;
    --text: #1f2937;
    --text-light: #4b5563;
    --text-muted: #6b7280;
    --bg: #ffffff;
    --bg-light: #f9fafb;
    --bg-gray: #f3f4f6;
    --border: #e5e7eb;
    --success: #10b981;
    --danger: #ef4444;
    --max-width: 1200px;
    --font-main: 'Inter', 'Segoe UI', Arial, sans-serif;
    --shadow-sm: 0 1px 3px rgba(0,0,0,0.08);
    --shadow-md: 0 4px 12px rgba(0,0,0,0.1);
    --shadow-lg: 0 8px 24px rgba(0,0,0,0.12);
    --radius: 8px;
}

html { font-size: 16px; scroll-behavior: smooth; }
body {
    font-family: var(--font-main);
    color: var(--text);
    background: var(--bg);
    line-height: 1.6;
}
a { text-decoration: none; color: inherit; transition: color 0.2s; }
a:hover { color: var(--primary); }
ul { list-style: none; }
.container { max-width: var(--max-width); margin: 0 auto; padding: 0 20px; }
.btn {
    display: inline-flex;
    align-items: center;
    justify-content: center;
    gap: 8px;
    padding: 12px 28px;
    border-radius: var(--radius);
    font-weight: 600;
    font-size: 0.95rem;
    cursor: pointer;
    border: none;
    transition: all 0.2s;
}
.btn-primary { background: var(--primary); color: #fff; }
.btn-primary:hover { background: var(--primary-dark); color: #fff; transform: translateY(-2px); }
.btn-accent { background: var(--accent); color: #fff; }
.btn-accent:hover { background: var(--accent-dark); color: #fff; transform: translateY(-2px); }
.btn-outline { background: transparent; border: 2px solid var(--primary); color: var(--primary); }
.btn-outline:hover { background: var(--primary); color: #fff; }

/* ==========================================
   TOP BAR
   ========================================== */
.top-bar {
    background: var(--primary-dark);
    color: #fff;
    font-size: 0.82rem;
    padding: 8px 0;
}
.top-bar .container {
    display: flex;
    justify-content: space-between;
    align-items: center;
}
.top-bar-left, .top-bar-right { display: flex; align-items: center; gap: 20px; }
.top-bar a { color: rgba(255,255,255,0.85); }
.top-bar a:hover { color: #fff; }
.hotline { font-weight: 700; color: var(--accent); }

/* ==========================================
   HEADER
   ========================================== */
.site-header {
    background: var(--bg);
    box-shadow: var(--shadow-sm);
    padding: 16px 0;
}
.header-main { display: flex; align-items: center; justify-content: space-between; gap: 30px; }
.logo {
    font-size: 1.8rem;
    font-weight: 800;
    color: var(--primary);
    letter-spacing: -1px;
}
.logo span { color: var(--accent); }
.logo small {
    display: block;
    font-size: 0.7rem;
    font-weight: 400;
    color: var(--text-muted);
    letter-spacing: 0.5px;
}
.header-search {
    flex: 1;
    max-width: 500px;
    display: flex;
}
.header-search input {
    flex: 1;
    padding: 10px 16px;
    border: 2px solid var(--border);
    border-right: none;
    border-radius: var(--radius) 0 0 var(--radius);
    font-size: 0.9rem;
    outline: none;
}
.header-search input:focus { border-color: var(--primary); }
.header-search button {
    padding: 10px 20px;
    background: var(--primary);
    color: #fff;
    border: none;
    border-radius: 0 var(--radius) var(--radius) 0;
    cursor: pointer;
}
.header-actions { display: flex; align-items: center; gap: 12px; }

/* ==========================================
   NAVIGATION
   ========================================== */
.main-nav {
    background: var(--bg);
    border-bottom: 2px solid var(--primary);
    position: sticky;
    top: 0;
    z-index: 1000;
}
.main-nav .container { display: flex; align-items: center; justify-content: space-between; }
.nav-menu { display: flex; gap: 0; }
.nav-menu > li > a {
    display: block;
    padding: 14px 18px;
    font-weight: 600;
    font-size: 0.9rem;
    color: var(--text);
    transition: all 0.2s;
    border-bottom: 3px solid transparent;
}
.nav-menu > li > a:hover,
.nav-menu > li.active > a {
    color: var(--primary);
    border-bottom-color: var(--primary);
}
.nav-dropdown {
    position: absolute;
    top: 100%;
    left: 0;
    background: var(--bg);
    min-width: 240px;
    box-shadow: var(--shadow-lg);
    border-radius: 0 0 var(--radius) var(--radius);
    opacity: 0;
    visibility: hidden;
    transform: translateY(10px);
    transition: all 0.25s;
}
.nav-menu li:hover .nav-dropdown {
    opacity: 1;
    visibility: visible;
    transform: translateY(0);
}
.nav-dropdown li a {
    display: block;
    padding: 12px 18px;
    font-size: 0.88rem;
    border-bottom: 1px solid var(--border);
}
.nav-dropdown li a:hover {
    background: var(--primary-light);
    color: var(--primary);
}

/* ==========================================
   HERO BANNER
   ========================================== */
.hero-section {
    background: linear-gradient(135deg, var(--primary) 0%, var(--primary-dark) 100%);
    color: #fff;
    padding: 60px 0;
    position: relative;
    overflow: hidden;
}
.hero-section::before {
    content: '';
    position: absolute;
    top: -50%;
    right: -10%;
    width: 500px;
    height: 500px;
    background: rgba(255,255,255,0.05);
    border-radius: 50%;
}
.hero-grid { display: grid; grid-template-columns: 1.2fr 1fr; gap: 40px; align-items: center; }
.hero-content h1 {
    font-size: 2.8rem;
    font-weight: 800;
    line-height: 1.2;
    margin-bottom: 16px;
}
.hero-content h1 span { color: var(--accent); }
.hero-content p {
    font-size: 1.1rem;
    opacity: 0.9;
    margin-bottom: 28px;
    line-height: 1.7;
}
.hero-btns { display: flex; gap: 16px; flex-wrap: wrap; }
.hero-stats {
    display: flex;
    gap: 32px;
    margin-top: 32px;
    padding-top: 24px;
    border-top: 1px solid rgba(255,255,255,0.2);
}
.stat-item { text-align: center; }
.stat-item .num { font-size: 2rem; font-weight: 800; color: var(--accent); }
.stat-item .label { font-size: 0.85rem; opacity: 0.8; }
.hero-features {
    background: rgba(255,255,255,0.1);
    border-radius: 12px;
    padding: 28px;
    backdrop-filter: blur(10px);
}
.hero-features h3 { font-size: 1.2rem; margin-bottom: 20px; }
.feature-list li {
    display: flex;
    align-items: center;
    gap: 12px;
    padding: 10px 0;
    font-size: 0.95rem;
}
.feature-list li::before {
    content: '✓';
    display: flex;
    align-items: center;
    justify-content: center;
    width: 24px;
    height: 24px;
    background: var(--success);
    border-radius: 50%;
    font-size: 0.75rem;
    color: #fff;
    flex-shrink: 0;
}

/* ==========================================
   SECTION HEADERS
   ========================================== */
.section-header {
    text-align: center;
    margin-bottom: 40px;
}
.section-title {
    font-size: 2rem;
    font-weight: 800;
    color: var(--text);
    margin-bottom: 8px;
}
.section-title span { color: var(--primary); }
.section-desc { color: var(--text-muted); font-size: 1rem; }

/* ==========================================
   COURSE CARDS
   ========================================== */
.courses-section { padding: 60px 0; background: var(--bg-light); }
.courses-grid {
    display: grid;
    grid-template-columns: repeat(3, 1fr);
    gap: 24px;
}
.course-card {
    background: var(--bg);
    border-radius: 12px;
    overflow: hidden;
    box-shadow: var(--shadow-sm);
    transition: transform 0.2s, box-shadow 0.2s;
}
.course-card:hover { transform: translateY(-6px); box-shadow: var(--shadow-lg); }
.course-thumb {
    height: 180px;
    background: linear-gradient(135deg, var(--primary-light) 0%, #dbeafe 100%);
    display: flex;
    align-items: center;
    justify-content: center;
    font-size: 4rem;
    position: relative;
}
.course-badge {
    position: absolute;
    top: 12px;
    right: 12px;
    background: var(--danger);
    color: #fff;
    padding: 4px 12px;
    border-radius: 20px;
    font-size: 0.72rem;
    font-weight: 700;
    text-transform: uppercase;
}
.course-badge.hot { background: var(--danger); }
.course-badge.new { background: var(--success); }
.course-body { padding: 20px; }
.course-grade {
    font-size: 0.75rem;
    font-weight: 600;
    color: var(--primary);
    background: var(--primary-light);
    padding: 4px 10px;
    border-radius: 4px;
    display: inline-block;
    margin-bottom: 10px;
}
.course-card h3 {
    font-size: 1.1rem;
    font-weight: 700;
    margin-bottom: 8px;
    line-height: 1.4;
}
.course-card h3 a { color: var(--text); }
.course-card h3 a:hover { color: var(--primary); }
.course-info { display: flex; align-items: center; gap: 12px; margin-bottom: 14px; }
.course-info span { font-size: 0.82rem; color: var(--text-muted); }
.course-footer {
    display: flex;
    justify-content: space-between;
    align-items: center;
    padding-top: 14px;
    border-top: 1px solid var(--border);
}
.course-price { font-size: 1.1rem; font-weight: 800; color: var(--primary); }
.course-price .old {
    font-size: 0.82rem;
    color: var(--text-muted);
    text-decoration: line-through;
    font-weight: 400;
    margin-left: 8px;
}

/* ==========================================
   TEACHER SECTION
   ========================================== */
.teachers-section { padding: 60px 0; }
.teachers-grid { display: grid; grid-template-columns: repeat(3, 1fr); gap: 28px; }
.teacher-card {
    text-align: center;
    padding: 32px 24px;
    background: var(--bg);
    border-radius: 12px;
    border: 2px solid var(--border);
    transition: all 0.2s;
}
.teacher-card:hover { border-color: var(--primary); box-shadow: var(--shadow-md); }
.teacher-avatar {
    width: 100px;
    height: 100px;
    border-radius: 50%;
    background: linear-gradient(135deg, var(--primary-light) 0%, #dbeafe 100%);
    display: flex;
    align-items: center;
    justify-content: center;
    font-size: 2.5rem;
    margin: 0 auto 18px auto;
}
.teacher-card h3 { font-size: 1.15rem; font-weight: 700; margin-bottom: 6px; }
.teacher-title { font-size: 0.85rem; color: var(--primary); font-weight: 600; margin-bottom: 12px; }
.teacher-desc { font-size: 0.88rem; color: var(--text-muted); line-height: 1.6; }

/* ==========================================
   WHY CHOOSE US
   ========================================== */
.why-section { padding: 60px 0; background: var(--bg-light); }
.why-grid { display: grid; grid-template-columns: repeat(4, 1fr); gap: 24px; }
.why-item {
    text-align: center;
    padding: 28px 20px;
    background: var(--bg);
    border-radius: 12px;
    box-shadow: var(--shadow-sm);
}
.why-icon {
    font-size: 2.5rem;
    margin-bottom: 16px;
}
.why-item h4 { font-size: 1.05rem; font-weight: 700; margin-bottom: 8px; }
.why-item p { font-size: 0.88rem; color: var(--text-muted); }

/* ==========================================
   TESTIMONIALS
   ========================================== */
.testimonials-section { padding: 60px 0; }
.testimonials-grid { display: grid; grid-template-columns: repeat(3, 1fr); gap: 24px; }
.testimonial-card {
    padding: 28px;
    background: var(--bg-light);
    border-radius: 12px;
    border-left: 4px solid var(--primary);
}
.testimonial-text { font-size: 0.92rem; font-style: italic; margin-bottom: 18px; line-height: 1.7; color: var(--text-light); }
.testimonial-author { display: flex; align-items: center; gap: 12px; }
.testimonial-avatar {
    width: 48px;
    height: 48px;
    border-radius: 50%;
    background: var(--primary-light);
    display: flex;
    align-items: center;
    justify-content: center;
    font-size: 1.2rem;
}
.testimonial-name { font-weight: 700; font-size: 0.92rem; }
.testimonial-role { font-size: 0.8rem; color: var(--text-muted); }

/* ==========================================
   CTA SECTION
   ========================================== */
.cta-section {
    background: linear-gradient(135deg, var(--primary) 0%, var(--primary-dark) 100%);
    color: #fff;
    text-align: center;
    padding: 60px 0;
}
.cta-section h2 { font-size: 2rem; font-weight: 800; margin-bottom: 12px; }
.cta-section p { font-size: 1.1rem; opacity: 0.9; margin-bottom: 28px; }
.cta-btns { display: flex; gap: 16px; justify-content: center; }

/* ==========================================
   FOOTER
   ========================================== */
.site-footer { background: #0f172a; color: rgba(255,255,255,0.7); padding: 50px 0 0; }
.footer-grid { display: grid; grid-template-columns: 1.5fr 1fr 1fr 1fr; gap: 40px; margin-bottom: 40px; }
.footer-about h4, .footer-col h4 { color: #fff; font-size: 1.05rem; font-weight: 700; margin-bottom: 18px; }
.footer-about p { font-size: 0.88rem; line-height: 1.7; margin-bottom: 16px; }
.footer-social { display: flex; gap: 10px; }
.footer-social a {
    width: 38px;
    height: 38px;
    background: rgba(255,255,255,0.1);
    border-radius: 6px;
    display: flex;
    align-items: center;
    justify-content: center;
    color: #fff;
    font-size: 0.85rem;
}
.footer-social a:hover { background: var(--primary); }
.footer-col ul { display: flex; flex-direction: column; gap: 10px; }
.footer-col ul li a { font-size: 0.88rem; color: rgba(255,255,255,0.65); }
.footer-col ul li a:hover { color: #fff; padding-left: 4px; }
.footer-bottom {
    border-top: 1px solid rgba(255,255,255,0.1);
    padding: 20px 0;
    text-align: center;
    font-size: 0.82rem;
    color: rgba(255,255,255,0.4);
}

/* ==========================================
   RESPONSIVE
   ========================================== */
@media (max-width: 1024px) {
    .courses-grid { grid-template-columns: repeat(2, 1fr); }
    .teachers-grid { grid-template-columns: repeat(2, 1fr); }
    .why-grid { grid-template-columns: repeat(2, 1fr); }
    .hero-grid { grid-template-columns: 1fr; }
    .footer-grid { grid-template-columns: repeat(2, 1fr); }
}
@media (max-width: 768px) {
    .courses-grid { grid-template-columns: 1fr; }
    .teachers-grid { grid-template-columns: 1fr; }
    .why-grid { grid-template-columns: 1fr; }
    .testimonials-grid { grid-template-columns: 1fr; }
    .hero-content h1 { font-size: 2rem; }
    .section-title { font-size: 1.6rem; }
    .footer-grid { grid-template-columns: 1fr; }
    .nav-menu { display: none; }
    .mobile-toggle { display: block; }
}