/* ==========================================
   AI REVIEW KIT - STYLE SYSTEM (DESIGN.MD)
   ========================================== */

:root {
    /* Color System */
    --bg-page: #FAFBFD;
    --bg-surface: #FFFFFF;
    --color-primary: #000000;
    --color-secondary: #0051d5;
    --color-secondary-hover: #003ea8;
    --color-text-main: #0b1c30;
    --color-text-muted: #45464d;
    --border-subtle: #E2E8F0;
    
    /* Semantic Colors */
    --accent-vibrant: #2563EB;
    --accent-teal: #0d9488;
    --accent-teal-bg: rgba(13, 148, 136, 0.06);
    --accent-purple: #7c3aed;
    --accent-purple-bg: rgba(124, 58, 237, 0.06);
    --accent-orange: #d97706;
    --accent-orange-bg: rgba(217, 119, 6, 0.06);
    --accent-blue-bg: rgba(0, 81, 213, 0.06);
    --color-error: #ba1a1a;
    --color-error-bg: #ffdad6;
    
    /* Spacing & Layout */
    --container-max: 840px;
    --section-gap: clamp(56px, 9vw, 96px);
    --gutter: 24px;
    --margin-page: clamp(20px, 5vw, 40px);
    
    /* Borders & Radius */
    --rounded-sm: 0.25rem;      /* 4px */
    --rounded-default: 0.5rem;  /* 8px */
    --rounded-md: 0.75rem;     /* 12px */
    --rounded-lg: 1rem;        /* 16px */
    --rounded-xl: 1.5rem;      /* 24px */
    --rounded-full: 9999px;
    
    /* Elevation & Shadows */
    --sh-sm: 0 1px 3px rgba(11, 28, 48, 0.04);
    --sh-md: 0 4px 20px rgba(11, 28, 48, 0.06);
    --sh-lg: 0 12px 36px rgba(11, 28, 48, 0.09);
    
    /* Typography Specs */
    --font-sans: 'Plus Jakarta Sans', system-ui, -apple-system, sans-serif;
    --ease: cubic-bezier(0.16, 1, 0.3, 1);
}

/* ==========================================
   BASE STYLES
   ========================================== */

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

html {
    scroll-behavior: smooth;
    scroll-padding-top: 80px;
}

body {
    font-family: var(--font-sans);
    background-color: var(--bg-page);
    color: var(--color-text-main);
    line-height: 1.7;
    -webkit-font-smoothing: antialiased;
    overflow-x: hidden;
}

img {
    max-width: 100%;
    height: auto;
    display: block;
}

a {
    color: var(--color-secondary);
    text-decoration: none;
    transition: all 0.3s var(--ease);
}

/* Utilities */
.ct {
    max-width: var(--container-max);
    margin: 0 auto;
    padding: 0 var(--margin-page);
}

section {
    padding: var(--section-gap) 0;
}

.bg-alt {
    background-color: #f3f6fc;
}

/* Typography Utilities */
.headline-xl {
    font-size: clamp(34px, 6vw, 50px);
    font-weight: 800;
    line-height: 1.15;
    letter-spacing: -0.02em;
    color: var(--color-primary);
}

.headline-lg {
    font-size: clamp(26px, 4vw, 32px);
    font-weight: 800;
    line-height: 1.25;
    letter-spacing: -0.01em;
    color: var(--color-primary);
}

.headline-sm {
    font-size: 20px;
    font-weight: 700;
    line-height: 1.4;
    color: var(--color-primary);
}

.body-lg {
    font-size: clamp(16px, 2.5vw, 18px);
    font-weight: 400;
    line-height: 1.7;
}

.body-md {
    font-size: 16px;
    font-weight: 400;
    line-height: 1.7;
}

.text-muted {
    color: var(--color-text-muted);
}

.font-semibold {
    font-weight: 600;
}

.font-bold {
    font-weight: 700;
}

.italic {
    font-style: italic;
}

/* Colors Accent */
.text-accent-vibrant {
    color: var(--color-secondary);
}

.text-accent-teal {
    color: var(--accent-teal);
}

.text-error {
    color: var(--color-error);
}

/* ==========================================
   BUTTONS
   ========================================== */

.btn {
    display: inline-flex;
    align-items: center;
    justify-content: center;
    padding: 12px 28px;
    font-size: 14px;
    font-weight: 700;
    border-radius: var(--rounded-md);
    transition: all 0.3s var(--ease);
    cursor: pointer;
    border: none;
    text-align: center;
    letter-spacing: 0.02em;
}

.btn-primary {
    background-color: var(--color-secondary);
    color: #ffffff;
    box-shadow: 0 4px 14px rgba(0, 81, 213, 0.25);
}

.btn-primary:hover {
    background-color: var(--color-secondary-hover);
    transform: translateY(-2px);
    box-shadow: 0 6px 20px rgba(0, 81, 213, 0.35);
    color: #ffffff;
}

.btn-secondary {
    background-color: #ffffff;
    color: var(--color-secondary);
    border: 1px solid var(--border-subtle);
    box-shadow: var(--sh-sm);
}

.btn-secondary:hover {
    border-color: var(--color-secondary);
    background-color: var(--accent-blue-bg);
    transform: translateY(-2px);
}

.btn-full {
    width: 100%;
    display: flex;
}

/* Shimmer primary CTA effect */
.btn-shimmer {
    position: relative;
    overflow: hidden;
}

.btn-shimmer::after {
    content: '';
    position: absolute;
    top: -50%;
    left: -60%;
    width: 30%;
    height: 200%;
    background: linear-gradient(
        to right,
        rgba(255, 255, 255, 0) 0%,
        rgba(255, 255, 255, 0.3) 50%,
        rgba(255, 255, 255, 0) 100%
    );
    transform: rotate(25deg);
    animation: shimmer-effect 4s infinite linear;
}

@keyframes shimmer-effect {
    0% { left: -60%; }
    30% { left: 140%; }
    100% { left: 140%; }
}

/* ==========================================
   HEADER / NAVIGATION
   ========================================== */

.nav {
    position: fixed;
    top: 0;
    left: 0;
    right: 0;
    z-index: 100;
    background: rgba(250, 251, 253, 0.85);
    backdrop-filter: blur(16px);
    -webkit-backdrop-filter: blur(16px);
    border-bottom: 1px solid transparent;
    transition: all 0.3s var(--ease);
}

.nav.scrolled {
    border-bottom-color: var(--border-subtle);
    box-shadow: var(--sh-sm);
}

.nav-inner {
    max-width: 1080px;
    margin: 0 auto;
    padding: 0 var(--margin-page);
    display: flex;
    align-items: center;
    justify-content: space-between;
    height: 72px;
}

.nav-brand {
    display: flex;
    align-items: center;
    gap: 12px;
}

.nav-brand img {
    width: 32px;
    height: 32px;
    border-radius: var(--rounded-default);
}

.nav-brand span {
    font-weight: 800;
    font-size: 16px;
    letter-spacing: -0.02em;
    color: var(--color-primary);
}

.nav-links {
    display: flex;
    align-items: center;
    gap: 32px;
}

.nav-links a {
    font-size: 14px;
    font-weight: 500;
    color: var(--color-text-muted);
}

.nav-links a:hover {
    color: var(--color-primary);
}

.nav-cta {
    font-size: 13px;
    font-weight: 700;
    padding: 8px 18px;
    background-color: var(--color-secondary);
    color: #ffffff;
    border-radius: var(--rounded-md);
    box-shadow: 0 4px 10px rgba(0, 81, 213, 0.2);
}

.nav-cta:hover {
    background-color: var(--color-secondary-hover);
    transform: translateY(-1px);
    color: #ffffff;
}

.nav-cta .mobile-text {
    display: none !important;
}

/* ==========================================
   HERO SECTION
   ========================================== */

#hero {
    min-height: 90vh;
    display: flex;
    align-items: center;
    padding-top: 145px;
    padding-bottom: 85px;
    background: 
        linear-gradient(180deg, rgba(250, 251, 253, 0.94) 0%, rgba(250, 251, 253, 0.88) 100%),
        url('hero-bg.png') center/cover no-repeat;
    position: relative;
    overflow: hidden;
}

.hero-glow {
    position: absolute;
    border-radius: var(--rounded-full);
    filter: blur(80px);
    z-index: 0;
    pointer-events: none;
}

.glow-1 {
    top: 10%;
    left: 15%;
    width: 250px;
    height: 250px;
    background: radial-gradient(circle, rgba(0, 81, 213, 0.12) 0%, rgba(13, 148, 136, 0.03) 70%, transparent 100%);
}

.glow-2 {
    bottom: 15%;
    right: 10%;
    width: 300px;
    height: 300px;
    background: radial-gradient(circle, rgba(124, 58, 237, 0.08) 0%, rgba(0, 81, 213, 0.03) 70%, transparent 100%);
}

.hero-content {
    position: relative;
    z-index: 1;
    text-align: center;
    display: flex;
    flex-direction: column;
    align-items: center;
    max-width: 760px;
    margin: 0 auto;
}

.badge-container {
    margin-bottom: 24px;
}

.hero-badge {
    background-color: var(--accent-blue-bg);
    color: var(--color-secondary);
    padding: 6px 16px;
    font-size: 12px;
    font-weight: 700;
    border-radius: var(--rounded-full);
    border: 1px solid rgba(0, 81, 213, 0.1);
    letter-spacing: 0.05em;
}

.hero-title {
    margin-bottom: 24px;
}

.hero-desc {
    color: var(--color-text-muted);
    margin-bottom: 36px;
    max-width: 620px;
}

.hero-cta-group {
    margin-bottom: 40px;
}

.hero-features {
    display: flex;
    justify-content: center;
    flex-wrap: wrap;
    gap: 32px;
    list-style: none;
}

.hero-features li {
    display: flex;
    align-items: center;
    gap: 8px;
    font-size: 14px;
    font-weight: 700;
    color: var(--color-text-muted);
}

.icon {
    display: inline-flex;
    align-items: center;
    justify-content: center;
    color: var(--color-secondary);
    flex-shrink: 0;
}

.icon svg {
    width: 20px;
    height: 20px;
}

/* ==========================================
   SECTION STANDARD HEADER
   ========================================== */

.section-header {
    text-align: center;
    max-width: 680px;
    margin: 0 auto 56px auto;
}

.sub-label {
    display: inline-block;
    font-size: 12px;
    font-weight: 700;
    letter-spacing: 0.1em;
    color: var(--color-secondary);
    margin-bottom: 12px;
}

.section-header h2 {
    margin-bottom: 16px;
}

.section-header p {
    color: var(--color-text-muted);
}

/* ==========================================
   PROBLEM SECTION (Vấn đề thực tế)
   ========================================== */

.problem-grid {
    display: grid;
    grid-template-columns: repeat(2, 1fr);
    gap: 24px;
}

.problem-card {
    background-color: var(--bg-surface);
    border: 1px solid var(--border-subtle);
    border-radius: var(--rounded-lg);
    padding: 32px;
    box-shadow: var(--sh-sm);
    transition: transform 0.3s var(--ease), box-shadow 0.3s var(--ease);
}

.problem-card:hover {
    transform: translateY(-4px);
    box-shadow: var(--sh-md);
}

.card-icon {
    margin-bottom: 16px;
    display: flex;
    align-items: center;
}

.card-icon svg {
    width: 26px;
    height: 26px;
}

.stroke-primary {
    stroke: var(--color-secondary);
}

.stroke-error {
    stroke: var(--color-error);
}

.stroke-teal {
    stroke: var(--accent-teal);
}

.card-alert {
    background-color: var(--accent-blue-bg);
    border-color: rgba(0, 81, 213, 0.15);
    grid-column: span 2;
}

.card-alert .card-icon svg {
    stroke: var(--color-error);
}

.quote-text {
    line-height: 1.8;
    letter-spacing: -0.005em;
    color: var(--color-text-main);
}

/* ==========================================
   FRAMEWORK SECTION (Cơ chế 4 lớp tư duy)
   ========================================== */

.framework-grid {
    display: grid;
    grid-template-columns: repeat(4, 1fr);
    gap: 20px;
}

.framework-card {
    background-color: var(--bg-surface);
    border: 1px solid var(--border-subtle);
    border-radius: var(--rounded-lg);
    padding: 32px 24px;
    box-shadow: var(--sh-sm);
    transition: transform 0.3s var(--ease), box-shadow 0.3s var(--ease);
    position: relative;
    overflow: hidden;
}

.framework-card:hover {
    transform: translateY(-6px);
    box-shadow: var(--sh-md);
}

.layer-number {
    font-size: 36px;
    font-weight: 800;
    margin-bottom: 20px;
    line-height: 1.0;
}

.framework-card.layer-01 { border-top: 4px solid var(--color-secondary); }
.framework-card.layer-01 .layer-number { color: var(--color-secondary); }

.framework-card.layer-02 { border-top: 4px solid var(--accent-teal); }
.framework-card.layer-02 .layer-number { color: var(--accent-teal); }

.framework-card.layer-03 { border-top: 4px solid var(--accent-purple); }
.framework-card.layer-03 .layer-number { color: var(--accent-purple); }

.framework-card.layer-04 { border-top: 4px solid var(--accent-orange); }
.framework-card.layer-04 .layer-number { color: var(--accent-orange); }

.framework-card h3 {
    margin-bottom: 12px;
}

.framework-card p {
    font-size: 14px;
    color: var(--color-text-muted);
    line-height: 1.6;
}

/* ==========================================
   OFFER SECTION
   ========================================== */

.offer-container {
    display: grid;
    grid-template-columns: 1.3fr 1fr;
    gap: 40px;
    align-items: start;
}

.offer-content {
    display: flex;
    flex-direction: column;
    gap: 28px;
}

.offer-intro {
    font-size: 16px;
    line-height: 1.7;
    color: var(--color-text-main);
}

.offer-intro em {
    font-style: normal;
    color: var(--color-secondary);
}

.offer-list {
    list-style: none;
    display: flex;
    flex-direction: column;
    gap: 20px;
}

.offer-list li {
    display: flex;
    gap: 16px;
    align-items: flex-start;
}

.list-icon {
    display: inline-flex;
    margin-top: 4px;
}

.list-icon svg {
    width: 20px;
    height: 20px;
}

/* Pricing Card Right Side */
.pricing-card {
    background-color: var(--bg-surface);
    border: 1px solid var(--border-subtle);
    border-radius: var(--rounded-xl);
    padding: 40px 32px;
    box-shadow: var(--sh-lg);
    text-align: center;
    position: relative;
    overflow: hidden;
}

.offer-footer-text {
    margin-top: 48px;
    border-top: 1px solid var(--border-subtle);
    padding-top: 32px;
    max-width: 100%;
}

.pricing-title {
    font-size: 18px;
    font-weight: 700;
    color: var(--color-text-muted);
    margin-bottom: 12px;
}

.price-value {
    font-size: 48px;
    font-weight: 800;
    color: var(--color-secondary);
    margin-bottom: 24px;
    letter-spacing: -0.02em;
}

.pricing-card .btn {
    margin-bottom: 20px;
}

.pricing-note {
    font-size: 14px;
    font-weight: 700;
    color: var(--color-text-main);
    line-height: 1.4;
    margin-bottom: 12px;
}

.pricing-subnote {
    font-size: 12px;
    color: var(--color-text-muted);
}

/* ==========================================
   AUDIENCE SECTION
   ========================================== */

.audience-grid {
    display: grid;
    grid-template-columns: repeat(2, 1fr);
    gap: 32px;
}

.audience-column {
    background-color: var(--bg-surface);
    border: 1px solid var(--border-subtle);
    border-radius: var(--rounded-lg);
    padding: 40px 32px;
    box-shadow: var(--sh-sm);
}

.column-title {
    font-size: 18px;
    font-weight: 700;
    margin-bottom: 24px;
    display: flex;
    align-items: center;
    gap: 8px;
}

.column-title .icon svg {
    width: 22px;
    height: 22px;
}

.audience-list {
    list-style: none;
    display: flex;
    flex-direction: column;
    gap: 16px;
}

.audience-list li {
    font-size: 15px;
    line-height: 1.6;
    position: relative;
    padding-left: 20px;
}

.audience-list li::before {
    content: "•";
    position: absolute;
    left: 0;
    color: var(--color-text-muted);
}

.column-yes .audience-list li::before {
    color: var(--accent-teal);
    display: none; /* Sử dụng SVG thay thế ở tiêu đề */
}

/* ==========================================
   FOUNDER SECTION
   ========================================== */

.founder-card {
    background-color: var(--bg-surface);
    border: 1px solid var(--border-subtle);
    border-top: 5px solid transparent;
    border-image: linear-gradient(to right, var(--color-secondary), var(--accent-teal)) 1;
    border-radius: var(--rounded-lg);
    padding: 48px;
    box-shadow: var(--sh-md);
}

.founder-header {
    display: flex;
    gap: 32px;
    align-items: flex-start;
    margin-bottom: 32px;
}

.founder-avatar {
    width: 110px;
    height: 110px;
    border-radius: var(--rounded-full);
    object-fit: cover;
    border: 4px solid var(--border-subtle);
}

.founder-title-info {
    flex: 1;
}

.founder-name {
    font-size: 24px;
    font-weight: 800;
    margin-bottom: 4px;
    letter-spacing: -0.01em;
}

.founder-subtitle {
    font-size: 14px;
    font-weight: 700;
    color: var(--color-secondary);
    margin-bottom: 12px;
}

.founder-achievements {
    font-size: 13px;
    line-height: 1.6;
    color: var(--color-text-muted);
}

.founder-body {
    display: flex;
    flex-direction: column;
    gap: 20px;
}

.founder-body p {
    font-size: 16px;
    line-height: 1.7;
    color: var(--color-text-muted);
}

/* ==========================================
   FAQ SECTION
   ========================================== */

.faq-list {
    display: flex;
    flex-direction: column;
    gap: 16px;
    max-width: 760px;
    margin: 0 auto;
}

.faq-item {
    background-color: var(--bg-surface);
    border: 1px solid var(--border-subtle);
    border-radius: var(--rounded-default);
    overflow: hidden;
    box-shadow: var(--sh-sm);
    transition: all 0.3s var(--ease);
}

.faq-question {
    width: 100%;
    display: flex;
    justify-content: space-between;
    align-items: center;
    padding: 20px 24px;
    background: none;
    border: none;
    font-size: 16px;
    font-weight: 700;
    color: var(--color-text-main);
    text-align: left;
    cursor: pointer;
    transition: background-color 0.3s var(--ease);
}

.faq-question:hover {
    background-color: var(--bg-page);
}

.faq-arrow {
    font-size: 10px;
    color: var(--color-text-muted);
    transition: transform 0.3s var(--ease);
}

.faq-answer {
    max-height: 0;
    overflow: hidden;
    transition: max-height 0.35s var(--ease), padding 0.35s var(--ease);
    padding: 0 24px;
}

.faq-answer p {
    padding-bottom: 20px;
    color: var(--color-text-muted);
    font-size: 15px;
}

/* Open State for JS */
.faq-item.active {
    border-color: rgba(0, 81, 213, 0.2);
}

.faq-item.active .faq-arrow {
    transform: rotate(180deg);
}

/* ==========================================
   FOOTER
   ========================================== */

.footer {
    background-color: #0b1c30;
    color: #ffffff;
    text-align: center;
    padding: 48px 0;
}

.footer-warning {
    font-size: 12px;
    color: rgba(255, 255, 255, 0.5);
    margin-bottom: 20px;
    max-width: 640px;
    margin-left: auto;
    margin-right: auto;
    line-height: 1.6;
}

.footer-copyright {
    font-size: 14px;
    font-weight: 500;
    color: rgba(255, 255, 255, 0.7);
}

/* ==========================================
   RESPONSIVE DESIGN
   ========================================== */

@media (max-width: 1024px) {
    .nav-links {
        display: none; /* Tránh cồng kềnh trên tablet/mobile */
    }
}

@media (max-width: 768px) {
    section {
        padding: 56px 0;
    }
    
    .problem-grid, .framework-grid, .audience-grid {
        grid-template-columns: 1fr;
    }
    
    .card-alert {
        grid-column: span 1 !important;
        padding: 24px 20px !important;
    }
    
    .offer-container {
        grid-template-columns: 1fr;
        gap: 32px;
    }
    
    .founder-header {
        flex-direction: column;
        align-items: center;
        text-align: center;
        gap: 20px;
    }
    
    .founder-card {
        padding: 32px 20px;
    }
    
    #hero {
        padding-top: 120px;
        padding-bottom: 60px;
    }
    
    .hero-features {
        flex-direction: column;
        align-items: center;
        gap: 16px;
    }

    .nav-brand span {
        font-size: 13px;
    }
    
    .nav-brand img {
        width: 28px;
        height: 28px;
    }
    
    .nav-cta {
        padding: 6px 12px;
        font-size: 11px;
        box-shadow: none;
    }
    
    .nav-cta .desktop-text {
        display: none !important;
    }
    
    .nav-cta .mobile-text {
        display: inline !important;
    }
}