/* ============================================
   AI PHYSICS LAB - MAIN STYLESHEET
   Modern, Professional, Premium Design
   ============================================ */

/* === ROOT VARIABLES === */
:root {
    /* Colors */
    --primary: #6366f1;
    --primary-dark: #4f46e5;
    --primary-light: #818cf8;
    --secondary: #8b5cf6;
    --accent: #ec4899;
    
    --success: #10b981;
    --warning: #f59e0b;
    --danger: #ef4444;
    --info: #3b82f6;
    
    --dark: #0f172a;
    --dark-light: #1e293b;
    --gray: #64748b;
    --gray-light: #cbd5e1;
    --gray-lighter: #f1f5f9;
    --white: #ffffff;
    
    --premium-gold: #fbbf24;
    --premium-gradient: linear-gradient(135deg, #fbbf24, #f59e0b);
    
    /* Typography */
    --font-primary: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, 'Helvetica Neue', Arial, sans-serif;
    --font-mono: 'SF Mono', Monaco, 'Cascadia Code', monospace;
    
    /* Spacing */
    --space-xs: 0.25rem;
    --space-sm: 0.5rem;
    --space-md: 1rem;
    --space-lg: 1.5rem;
    --space-xl: 2rem;
    --space-2xl: 3rem;
    --space-3xl: 4rem;
    
    /* Border Radius */
    --radius-sm: 0.375rem;
    --radius-md: 0.5rem;
    --radius-lg: 0.75rem;
    --radius-xl: 1rem;
    --radius-full: 9999px;
    
    /* Shadows */
    --shadow-sm: 0 1px 2px 0 rgba(0, 0, 0, 0.05);
    --shadow-md: 0 4px 6px -1px rgba(0, 0, 0, 0.1);
    --shadow-lg: 0 10px 15px -3px rgba(0, 0, 0, 0.1);
    --shadow-xl: 0 20px 25px -5px rgba(0, 0, 0, 0.1);
    --shadow-2xl: 0 25px 50px -12px rgba(0, 0, 0, 0.25);
    
    /* Animations */
    --transition-fast: 150ms cubic-bezier(0.4, 0, 0.2, 1);
    --transition-base: 250ms cubic-bezier(0.4, 0, 0.2, 1);
    --transition-slow: 350ms cubic-bezier(0.4, 0, 0.2, 1);
}

/* === RESET & BASE === */
* {
    margin: 0;
    padding: 0;
    box-sizing: border-box;
}

html {
    scroll-behavior: smooth;
}

body {
    font-family: var(--font-primary);
    font-size: 16px;
    line-height: 1.6;
    color: var(--dark);
    background: var(--white);
    overflow-x: hidden;
}

h1, h2, h3, h4, h5, h6 {
    font-weight: 700;
    line-height: 1.2;
    margin-bottom: var(--space-md);
}

h1 { font-size: 3rem; }
h2 { font-size: 2.25rem; }
h3 { font-size: 1.875rem; }
h4 { font-size: 1.5rem; }
h5 { font-size: 1.25rem; }
h6 { font-size: 1rem; }

p {
    margin-bottom: var(--space-md);
}

a {
    color: var(--primary);
    text-decoration: none;
    transition: all var(--transition-base);
}

a:hover {
    color: var(--primary-dark);
}

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

/* === UTILITY CLASSES === */
.container {
    max-width: 1200px;
    margin: 0 auto;
    padding: 0 var(--space-lg);
}

.gradient-text {
    background: linear-gradient(135deg, var(--primary), var(--secondary));
    -webkit-background-clip: text;
    -webkit-text-fill-color: transparent;
    background-clip: text;
}

/* === BUTTONS === */
.btn {
    display: inline-flex;
    align-items: center;
    justify-content: center;
    gap: var(--space-sm);
    padding: 0.75rem 1.5rem;
    font-size: 1rem;
    font-weight: 600;
    border: none;
    border-radius: var(--radius-lg);
    cursor: pointer;
    transition: all var(--transition-base);
    text-decoration: none;
    white-space: nowrap;
}

.btn-primary {
    background: var(--primary);
    color: var(--white);
}

.btn-primary:hover {
    background: var(--primary-dark);
    transform: translateY(-2px);
    box-shadow: var(--shadow-lg);
}

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

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

.btn-premium {
    background: var(--premium-gradient);
    color: var(--dark);
    font-weight: 700;
}

.btn-premium:hover {
    transform: translateY(-2px);
    box-shadow: 0 10px 25px rgba(251, 191, 36, 0.3);
}

.btn-white {
    background: var(--white);
    color: var(--primary);
}

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

.btn-large {
    padding: 1rem 2rem;
    font-size: 1.125rem;
}

.btn-block {
    width: 100%;
}

.btn-icon {
    font-size: 1.25rem;
}

/* === NAVBAR === */
.navbar {
    position: sticky;
    top: 0;
    z-index: 1000;
    background: rgba(255, 255, 255, 0.95);
    backdrop-filter: blur(10px);
    border-bottom: 1px solid var(--gray-lighter);
    padding: var(--space-md) 0;
}

.nav-container {
    display: flex;
    align-items: center;
    justify-content: space-between;
}

.logo {
    display: flex;
    align-items: center;
    gap: var(--space-sm);
    font-size: 1.5rem;
    font-weight: 700;
    color: var(--dark);
}

.logo-icon {
    font-size: 2rem;
}

.nav-menu {
    display: flex;
    gap: var(--space-xl);
}

.nav-link {
    color: var(--gray);
    font-weight: 500;
    transition: color var(--transition-base);
}

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

.nav-actions {
    display: flex;
    align-items: center;
    gap: var(--space-md);
}

.mobile-menu-toggle {
    display: none;
    flex-direction: column;
    gap: 4px;
    background: none;
    border: none;
    cursor: pointer;
}

.mobile-menu-toggle span {
    width: 24px;
    height: 2px;
    background: var(--dark);
    transition: all var(--transition-base);
}

/* === HERO SECTION === */
.hero {
    position: relative;
    padding: var(--space-3xl) 0;
    background: linear-gradient(135deg, #667eea 0%, #764ba2 100%);
    color: var(--white);
    overflow: hidden;
}

.hero-background {
    position: absolute;
    inset: 0;
    overflow: hidden;
}

.particle {
    position: absolute;
    width: 300px;
    height: 300px;
    border-radius: 50%;
    background: rgba(255, 255, 255, 0.1);
    animation: float 20s infinite ease-in-out;
}

.particle:nth-child(1) {
    top: 10%;
    left: 10%;
    animation-delay: 0s;
}

.particle:nth-child(2) {
    top: 60%;
    right: 10%;
    animation-delay: 7s;
}

.particle:nth-child(3) {
    bottom: 10%;
    left: 50%;
    animation-delay: 14s;
}

@keyframes float {
    0%, 100% { transform: translate(0, 0) scale(1); }
    33% { transform: translate(30px, -50px) scale(1.1); }
    66% { transform: translate(-20px, 20px) scale(0.9); }
}

.hero-container {
    position: relative;
    z-index: 1;
    display: grid;
    grid-template-columns: 1fr 1fr;
    gap: var(--space-3xl);
    align-items: center;
}

.hero-badge {
    display: inline-flex;
    align-items: center;
    gap: var(--space-sm);
    padding: var(--space-sm) var(--space-lg);
    background: rgba(255, 255, 255, 0.2);
    backdrop-filter: blur(10px);
    border-radius: var(--radius-full);
    font-size: 0.875rem;
    font-weight: 600;
    margin-bottom: var(--space-lg);
}

.badge-icon {
    font-size: 1.25rem;
}

.hero-title {
    font-size: 3.5rem;
    font-weight: 800;
    line-height: 1.1;
    margin-bottom: var(--space-lg);
}

.hero-description {
    font-size: 1.25rem;
    opacity: 0.95;
    margin-bottom: var(--space-xl);
    line-height: 1.8;
}

.hero-stats {
    display: flex;
    gap: var(--space-2xl);
    margin-bottom: var(--space-2xl);
}

.stat-item {
    text-align: center;
}

.stat-number {
    display: block;
    font-size: 2.5rem;
    font-weight: 800;
    line-height: 1;
}

.stat-label {
    font-size: 0.875rem;
    opacity: 0.9;
}

.hero-cta {
    display: flex;
    gap: var(--space-lg);
    margin-bottom: var(--space-xl);
}

.hero-trust {
    opacity: 0.9;
}

.trust-text {
    font-size: 0.875rem;
}

/* Hero Visual */
.hero-visual {
    position: relative;
}

.visual-container {
    position: relative;
    width: 100%;
    height: 500px;
}

.floating-card {
    position: absolute;
    background: rgba(255, 255, 255, 0.95);
    backdrop-filter: blur(10px);
    padding: var(--space-lg);
    border-radius: var(--radius-xl);
    box-shadow: var(--shadow-2xl);
    display: flex;
    gap: var(--space-md);
    animation: float-card 6s infinite ease-in-out;
}

.floating-card .card-icon {
    font-size: 2rem;
}

.floating-card .card-content {
    color: var(--dark);
}

.floating-card .card-title {
    font-weight: 600;
    font-size: 1rem;
    margin: 0;
}

.floating-card .card-desc {
    font-size: 0.875rem;
    color: var(--gray);
    margin: 0;
}

.card-1 {
    top: 10%;
    left: 0;
    animation-delay: 0s;
}

.card-2 {
    top: 40%;
    right: 0;
    animation-delay: 2s;
}

.card-3 {
    bottom: 10%;
    left: 20%;
    animation-delay: 4s;
}

@keyframes float-card {
    0%, 100% { transform: translateY(0); }
    50% { transform: translateY(-20px); }
}

.central-visual {
    position: absolute;
    top: 50%;
    left: 50%;
    transform: translate(-50%, -50%);
}

.pendulum-container {
    position: relative;
    width: 200px;
    height: 300px;
}

.pendulum-string {
    position: absolute;
    top: 0;
    left: 50%;
    width: 2px;
    height: 200px;
    background: var(--white);
    transform-origin: top center;
    animation: swing 2s infinite ease-in-out;
}

.pendulum-bob {
    position: absolute;
    bottom: 0;
    left: 50%;
    width: 40px;
    height: 40px;
    background: var(--white);
    border-radius: 50%;
    transform: translateX(-50%);
    box-shadow: var(--shadow-xl);
    animation: swing 2s infinite ease-in-out;
}

@keyframes swing {
    0%, 100% { transform: rotate(-25deg); }
    50% { transform: rotate(25deg); }
}

/* === SECTIONS === */
.experiments-section,
.premium-preview,
.features-section,
.pricing-section {
    padding: var(--space-3xl) 0;
}

.section-header {
    text-align: center;
    margin-bottom: var(--space-3xl);
}

.section-badge {
    display: inline-block;
    padding: var(--space-sm) var(--space-lg);
    background: var(--gray-lighter);
    color: var(--primary);
    border-radius: var(--radius-full);
    font-size: 0.875rem;
    font-weight: 600;
    margin-bottom: var(--space-md);
}

.premium-badge {
    background: var(--premium-gradient);
    color: var(--dark);
}

.section-title {
    font-size: 2.5rem;
    font-weight: 800;
    margin-bottom: var(--space-md);
}

.section-description {
    font-size: 1.125rem;
    color: var(--gray);
    max-width: 600px;
    margin: 0 auto;
}

/* === EXPERIMENT CARDS === */
.experiments-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(320px, 1fr));
    gap: var(--space-xl);
}

.experiment-card {
    position: relative;
    background: var(--white);
    padding: var(--space-xl);
    border-radius: var(--radius-xl);
    box-shadow: var(--shadow-md);
    transition: all var(--transition-base);
    border: 2px solid transparent;
}

.experiment-card:hover {
    transform: translateY(-8px);
    box-shadow: var(--shadow-2xl);
}

.free-card {
    border-color: var(--success);
}

.premium-card {
    border-color: var(--premium-gold);
}

.card-badge {
    position: absolute;
    top: var(--space-md);
    right: var(--space-md);
    padding: var(--space-xs) var(--space-md);
    border-radius: var(--radius-full);
    font-size: 0.75rem;
    font-weight: 700;
    text-transform: uppercase;
}

.free-badge {
    background: var(--success);
    color: var(--white);
}

.card-icon-large {
    font-size: 4rem;
    margin-bottom: var(--space-lg);
}

.card-title {
    font-size: 1.5rem;
    font-weight: 700;
    margin-bottom: var(--space-md);
}

.card-description {
    color: var(--gray);
    margin-bottom: var(--space-lg);
    line-height: 1.6;
}

.card-features {
    display: flex;
    flex-wrap: wrap;
    gap: var(--space-sm);
    margin-bottom: var(--space-lg);
}

.feature-tag {
    padding: var(--space-xs) var(--space-md);
    background: var(--gray-lighter);
    color: var(--gray);
    border-radius: var(--radius-full);
    font-size: 0.75rem;
    font-weight: 600;
}

/* Premium Card Lock Overlay */
.locked {
    position: relative;
}

.lock-overlay {
    position: absolute;
    inset: 0;
    background: rgba(15, 23, 42, 0.8);
    backdrop-filter: blur(4px);
    border-radius: var(--radius-xl);
    display: flex;
    flex-direction: column;
    align-items: center;
    justify-content: center;
    z-index: 10;
}

.lock-icon {
    font-size: 4rem;
    margin-bottom: var(--space-md);
}

.lock-text {
    color: var(--white);
    font-weight: 600;
    font-size: 1.125rem;
}

/* === FEATURES GRID === */
.features-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(300px, 1fr));
    gap: var(--space-2xl);
}

.feature-card {
    text-align: center;
    padding: var(--space-xl);
}

.feature-icon {
    font-size: 4rem;
    margin-bottom: var(--space-lg);
}

.feature-title {
    font-size: 1.5rem;
    font-weight: 700;
    margin-bottom: var(--space-md);
}

.feature-description {
    color: var(--gray);
    line-height: 1.8;
}

/* === PRICING === */
.pricing-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(300px, 1fr));
    gap: var(--space-2xl);
    margin-bottom: var(--space-2xl);
}

.pricing-card {
    position: relative;
    background: var(--white);
    padding: var(--space-2xl);
    border-radius: var(--radius-xl);
    border: 2px solid var(--gray-lighter);
    transition: all var(--transition-base);
}

.pricing-card.featured {
    border-color: var(--primary);
    box-shadow: var(--shadow-2xl);
    transform: scale(1.05);
}

.popular-badge {
    position: absolute;
    top: -12px;
    left: 50%;
    transform: translateX(-50%);
    padding: var(--space-sm) var(--space-lg);
    background: var(--primary);
    color: var(--white);
    border-radius: var(--radius-full);
    font-size: 0.75rem;
    font-weight: 700;
}

.pricing-header {
    text-align: center;
    padding-bottom: var(--space-xl);
    border-bottom: 2px solid var(--gray-lighter);
    margin-bottom: var(--space-xl);
}

.plan-name {
    font-size: 1.5rem;
    margin-bottom: var(--space-md);
}

.plan-price {
    margin-bottom: var(--space-md);
}

.price {
    font-size: 3rem;
    font-weight: 800;
    color: var(--primary);
}

.period {
    color: var(--gray);
    font-size: 1rem;
}

.plan-description {
    color: var(--gray);
    margin: 0;
}

.plan-features {
    list-style: none;
    margin-bottom: var(--space-xl);
}

.plan-features li {
    padding: var(--space-md) 0;
    border-bottom: 1px solid var(--gray-lighter);
}

.feature-included {
    color: var(--dark);
    font-weight: 500;
}

.feature-excluded {
    color: var(--gray-light);
}

.feature-highlight {
    color: var(--premium-gold);
    font-weight: 700;
}

.pricing-trust {
    text-align: center;
    color: var(--gray);
    font-size: 0.875rem;
}

/* === CTA SECTION === */
.cta-section {
    padding: var(--space-3xl) 0;
    background: linear-gradient(135deg, var(--primary), var(--secondary));
    color: var(--white);
    text-align: center;
}

.cta-title {
    font-size: 3rem;
    font-weight: 800;
    margin-bottom: var(--space-lg);
}

.cta-description {
    font-size: 1.25rem;
    opacity: 0.95;
    margin-bottom: var(--space-2xl);
    max-width: 700px;
    margin-left: auto;
    margin-right: auto;
}

.cta-buttons {
    display: flex;
    gap: var(--space-lg);
    justify-content: center;
}

/* === FOOTER === */
.footer {
    background: var(--dark);
    color: var(--gray-light);
    padding: var(--space-3xl) 0 var(--space-xl);
}

.footer-grid {
    display: grid;
    grid-template-columns: 2fr repeat(3, 1fr);
    gap: var(--space-2xl);
    margin-bottom: var(--space-2xl);
}

.footer-logo {
    display: flex;
    align-items: center;
    gap: var(--space-sm);
    font-size: 1.5rem;
    font-weight: 700;
    color: var(--white);
    margin-bottom: var(--space-lg);
}

.footer-description {
    line-height: 1.8;
}

.footer-title {
    color: var(--white);
    font-size: 1.125rem;
    margin-bottom: var(--space-lg);
}

.footer-links {
    list-style: none;
}

.footer-links li {
    margin-bottom: var(--space-md);
}

.footer-links a {
    color: var(--gray-light);
    transition: color var(--transition-base);
}

.footer-links a:hover {
    color: var(--white);
}

.footer-bottom {
    display: flex;
    justify-content: space-between;
    align-items: center;
    padding-top: var(--space-xl);
    border-top: 1px solid var(--dark-light);
}

.footer-social {
    display: flex;
    gap: var(--space-lg);
}

.footer-social a {
    font-size: 1.5rem;
    transition: transform var(--transition-base);
}

.footer-social a:hover {
    transform: scale(1.2);
}

/* === FLOATING AI CHAT BUTTON === */
.ai-chat-fab {
    position: fixed;
    bottom: 30px;
    right: 30px;
    display: flex;
    align-items: center;
    gap: var(--space-sm);
    padding: var(--space-lg) var(--space-xl);
    background: var(--primary);
    color: var(--white);
    border: none;
    border-radius: var(--radius-full);
    font-size: 1rem;
    font-weight: 600;
    box-shadow: var(--shadow-2xl);
    cursor: pointer;
    transition: all var(--transition-base);
    z-index: 999;
    animation: pulse-fab 2s infinite;
}

.ai-chat-fab:hover {
    transform: scale(1.1);
    box-shadow: 0 20px 40px rgba(99, 102, 241, 0.4);
}

.fab-icon {
    font-size: 1.5rem;
}

@keyframes pulse-fab {
    0%, 100% { box-shadow: 0 10px 30px rgba(99, 102, 241, 0.3); }
    50% { box-shadow: 0 15px 40px rgba(99, 102, 241, 0.5); }
}

/* === RESPONSIVE DESIGN === */
@media (max-width: 1024px) {
    .hero-container {
        grid-template-columns: 1fr;
    }
    
    .hero-visual {
        display: none;
    }
    
    .footer-grid {
        grid-template-columns: repeat(2, 1fr);
    }
}

@media (max-width: 768px) {
    h1 { font-size: 2rem; }
    h2 { font-size: 1.75rem; }
    
    .hero-title {
        font-size: 2.5rem;
    }
    
    .section-title {
        font-size: 2rem;
    }
    
    .nav-menu {
        display: none;
    }
    
    .mobile-menu-toggle {
        display: flex;
    }
    
    .nav-menu.active {
        display: flex;
        flex-direction: column;
        position: absolute;
        top: 100%;
        left: 0;
        right: 0;
        background: var(--white);
        padding: var(--space-lg);
        box-shadow: var(--shadow-lg);
    }
    
    .hero-cta {
        flex-direction: column;
    }
    
    .hero-stats {
        flex-wrap: wrap;
    }
    
    .cta-buttons {
        flex-direction: column;
    }
    
    .experiments-grid {
        grid-template-columns: 1fr;
    }
    
    .pricing-grid {
        grid-template-columns: 1fr;
    }
    
    .pricing-card.featured {
        transform: scale(1);
    }
    
    .footer-grid {
        grid-template-columns: 1fr;
    }
    
    .footer-bottom {
        flex-direction: column;
        gap: var(--space-lg);
        text-align: center;
    }
    
    .ai-chat-fab {
        bottom: 20px;
        right: 20px;
        padding: var(--space-md) var(--space-lg);
    }
    
    .fab-text {
        display: none;
    }
}

/* === UTILITY CLASSES === */
.text-center { text-align: center; }
.text-left { text-align: left; }
.text-right { text-align: right; }

.mt-0 { margin-top: 0; }
.mt-1 { margin-top: var(--space-sm); }
.mt-2 { margin-top: var(--space-md); }
.mt-3 { margin-top: var(--space-lg); }

.mb-0 { margin-bottom: 0; }
.mb-1 { margin-bottom: var(--space-sm); }
.mb-2 { margin-bottom: var(--space-md); }
.mb-3 { margin-bottom: var(--space-lg); }
/* ============================================
   EDUCATIONAL CONTENT SECTIONS
   For Experiment Pages, Theory, Blog Posts
   ============================================ */

/* === INTRODUCTION SECTION === */
.intro-section {
    max-width: 900px;
    margin: 40px auto;
    padding: 35px;
    background: linear-gradient(135deg, #f0f9ff 0%, #e0f2fe 100%);
    border-radius: 16px;
    border-left: 6px solid var(--primary);
    box-shadow: var(--shadow-md);
}

.intro-section h2 {
    color: #1e40af;
    font-size: 1.9rem;
    margin-bottom: 18px;
    display: flex;
    align-items: center;
    gap: 12px;
}

.intro-section p {
    font-size: 1.1rem;
    line-height: 1.8;
    color: #334155;
    margin-bottom: 15px;
}

/* === THEORY SECTION === */
.theory-section {
    max-width: 900px;
    margin: 50px auto;
    padding: 40px;
    background: var(--white);
    border-radius: 16px;
    box-shadow: var(--shadow-lg);
    border: 1px solid var(--gray-lighter);
}

.theory-section h2 {
    color: var(--dark);
    font-size: 2rem;
    margin-bottom: 25px;
    border-bottom: 4px solid var(--primary);
    padding-bottom: 15px;
    display: inline-block;
}

.theory-section h3 {
    color: #334155;
    font-size: 1.4rem;
    margin-top: 30px;
    margin-bottom: 15px;
    padding-left: 15px;
    border-left: 4px solid var(--secondary);
}

.theory-section p {
    font-size: 1.05rem;
    line-height: 1.75;
    color: #475569;
    margin-bottom: 20px;
}

.theory-section ul,
.theory-section ol {
    margin: 20px 0;
    padding-left: 30px;
}

.theory-section li {
    font-size: 1.05rem;
    line-height: 1.7;
    color: #475569;
    margin-bottom: 12px;
}

/* === FORMULA BOX === */
.formula-box {
    background: linear-gradient(135deg, #fef3c7 0%, #fde68a 100%);
    border: 3px solid #fbbf24;
    border-radius: 12px;
    padding: 25px;
    margin: 30px 0;
    text-align: center;
    box-shadow: var(--shadow-md);
}

.formula-box .formula {
    font-family: var(--font-mono);
    font-size: 1.5rem;
    font-weight: 700;
    color: #92400e;
    margin-bottom: 15px;
}

.formula-box .formula-desc {
    font-size: 0.95rem;
    color: #78350f;
    margin-top: 10px;
}

/* === KEY TOPICS BOX === */
.key-topics {
    background: linear-gradient(135deg, #f1f5f9 0%, #e2e8f0 100%);
    padding: 30px;
    border-radius: 14px;
    margin: 35px auto;
    max-width: 900px;
    box-shadow: var(--shadow-md);
}

.key-topics h3 {
    color: var(--dark);
    font-size: 1.5rem;
    margin-bottom: 20px;
    display: flex;
    align-items: center;
    gap: 10px;
}

.key-topics ul {
    list-style: none;
    padding: 0;
    margin: 0;
}

.key-topics li {
    padding: 14px 0 14px 40px;
    position: relative;
    color: #334155;
    font-size: 1.08rem;
    line-height: 1.6;
    border-bottom: 1px solid #cbd5e1;
}

.key-topics li:last-child {
    border-bottom: none;
}

.key-topics li:before {
    content: "✓";
    position: absolute;
    left: 0;
    top: 12px;
    color: var(--success);
    font-weight: 900;
    font-size: 1.5rem;
}

/* === OBJECTIVES SECTION === */
.objectives {
    background: linear-gradient(135deg, #dbeafe 0%, #bfdbfe 100%);
    padding: 35px;
    border-radius: 14px;
    margin: 35px auto;
    max-width: 900px;
    box-shadow: var(--shadow-md);
    border: 2px solid #93c5fd;
}

.objectives h2 {
    color: #1e40af;
    font-size: 1.75rem;
    margin-bottom: 22px;
    text-align: center;
}

.objectives ul {
    list-style: none;
    padding: 0;
    margin: 0;
}

.objectives li {
    padding: 15px 0 15px 45px;
    position: relative;
    font-size: 1.08rem;
    color: #1e40af;
    line-height: 1.7;
    font-weight: 500;
}

.objectives li:before {
    content: "🎯";
    position: absolute;
    left: 0;
    top: 12px;
    font-size: 1.4rem;
}

/* === PROCEDURE SECTION === */
.procedure-section {
    max-width: 900px;
    margin: 50px auto;
    padding: 40px;
    background: var(--white);
    border-radius: 16px;
    box-shadow: var(--shadow-lg);
}

.procedure-section h2 {
    color: var(--dark);
    font-size: 2rem;
    margin-bottom: 25px;
}

.procedure-section ol {
    counter-reset: step-counter;
    list-style: none;
    padding: 0;
}

.procedure-section li {
    counter-increment: step-counter;
    padding: 20px;
    margin-bottom: 20px;
    background: var(--gray-lighter);
    border-radius: 10px;
    position: relative;
    padding-left: 70px;
}

.procedure-section li:before {
    content: counter(step-counter);
    position: absolute;
    left: 20px;
    top: 50%;
    transform: translateY(-50%);
    width: 40px;
    height: 40px;
    background: var(--primary);
    color: var(--white);
    border-radius: 50%;
    display: flex;
    align-items: center;
    justify-content: center;
    font-weight: 700;
    font-size: 1.2rem;
}

/* === VIVA SECTION === */
.viva-section {
    max-width: 900px;
    margin: 60px auto;
    padding: 0 20px;
}

.viva-section h2 {
    color: var(--dark);
    font-size: 2.2rem;
    margin-bottom: 35px;
    text-align: center;
    position: relative;
    padding-bottom: 15px;
}

.viva-section h2:after {
    content: "";
    position: absolute;
    bottom: 0;
    left: 50%;
    transform: translateX(-50%);
    width: 100px;
    height: 4px;
    background: var(--secondary);
}

/* === VIVA Q&A CARDS === */
.viva-qa {
    background: var(--white);
    border: 2px solid #e9d5ff;
    border-left: 6px solid var(--secondary);
    border-radius: 14px;
    padding: 30px;
    margin-bottom: 25px;
    transition: all var(--transition-base);
    box-shadow: var(--shadow-sm);
}

.viva-qa:hover {
    box-shadow: var(--shadow-xl);
    transform: translateY(-4px);
    border-left-color: #a855f7;
}

.viva-qa h3 {
    color: var(--secondary);
    font-size: 1.25rem;
    margin-bottom: 15px;
    display: flex;
    align-items: flex-start;
    gap: 12px;
    line-height: 1.5;
}

.viva-qa h3:before {
    content: "Q:";
    font-weight: 800;
    color: #a855f7;
    font-size: 1.4rem;
    flex-shrink: 0;
}

.viva-qa p {
    color: #475569;
    font-size: 1.05rem;
    line-height: 1.8;
    margin: 0;
    padding-left: 35px;
}

.viva-qa p:before {
    content: "A: ";
    font-weight: 700;
    color: var(--success);
    margin-left: -35px;
    margin-right: 8px;
}

/* === APPLICATIONS SECTION === */
.applications-section {
    max-width: 900px;
    margin: 50px auto;
    padding: 35px;
    background: linear-gradient(135deg, #fef3c7 0%, #fde68a 100%);
    border-radius: 16px;
    box-shadow: var(--shadow-md);
}

.applications-section h2 {
    color: #92400e;
    font-size: 1.9rem;
    margin-bottom: 20px;
}

.applications-section ul {
    list-style: none;
    padding: 0;
}

.applications-section li {
    padding: 15px 0 15px 40px;
    position: relative;
    color: #78350f;
    font-size: 1.05rem;
    line-height: 1.7;
}

.applications-section li:before {
    content: "💡";
    position: absolute;
    left: 0;
    top: 12px;
    font-size: 1.3rem;
}

/* === PRECAUTIONS BOX === */
.precautions-box {
    background: #fee2e2;
    border: 2px solid #fca5a5;
    border-radius: 12px;
    padding: 25px;
    margin: 30px auto;
    max-width: 900px;
}

.precautions-box h3 {
    color: #991b1b;
    font-size: 1.4rem;
    margin-bottom: 15px;
    display: flex;
    align-items: center;
    gap: 10px;
}

.precautions-box h3:before {
    content: "⚠️";
    font-size: 1.5rem;
}

.precautions-box ul {
    list-style: none;
    padding: 0;
}

.precautions-box li {
    padding: 10px 0 10px 30px;
    position: relative;
    color: #7f1d1d;
    font-size: 1rem;
}

.precautions-box li:before {
    content: "•";
    position: absolute;
    left: 0;
    color: #dc2626;
    font-size: 1.5rem;
    font-weight: 900;
}

/* === INFO BOXES (General Purpose) === */
.info-box {
    padding: 20px 25px;
    border-radius: 10px;
    margin: 25px auto;
    max-width: 900px;
    border-left: 5px solid;
}

.info-box.info {
    background: #dbeafe;
    border-color: var(--info);
    color: #1e3a8a;
}

.info-box.success {
    background: #d1fae5;
    border-color: var(--success);
    color: #065f46;
}

.info-box.warning {
    background: #fef3c7;
    border-color: var(--warning);
    color: #78350f;
}

.info-box.danger {
    background: #fee2e2;
    border-color: var(--danger);
    color: #991b1b;
}

/* === CONTENT WRAPPER === */
.content-wrapper {
    max-width: 900px;
    margin: 0 auto;
    padding: 40px 20px;
}

.content-block {
    margin-bottom: 40px;
}

.content-block h2 {
    color: var(--dark);
    font-size: 1.8rem;
    margin-bottom: 20px;
}

.content-block p {
    font-size: 1.05rem;
    line-height: 1.8;
    color: #475569;
    margin-bottom: 15px;
}

/* === MOBILE RESPONSIVE === */
@media (max-width: 768px) {
    .intro-section,
    .theory-section,
    .key-topics,
    .objectives,
    .procedure-section,
    .applications-section {
        padding: 25px 20px;
        margin: 25px 15px;
    }
    
    .intro-section h2,
    .theory-section h2 {
        font-size: 1.5rem;
    }
    
    .theory-section h3 {
        font-size: 1.2rem;
    }
    
    .formula-box {
        padding: 20px 15px;
    }
    
    .formula-box .formula {
        font-size: 1.2rem;
    }
    
    .viva-section {
        padding: 0 15px;
    }
    
    .viva-section h2 {
        font-size: 1.8rem;
    }
    
    .viva-qa {
        padding: 20px 18px;
    }
    
    .viva-qa h3 {
        font-size: 1.1rem;
    }
    
    .viva-qa p {
        font-size: 1rem;
        padding-left: 25px;
    }
    
    .procedure-section li {
        padding-left: 65px;
    }
    
    .procedure-section li:before {
        width: 35px;
        height: 35px;
        font-size: 1rem;
    }
}

/* === PRINT STYLES === */
@media print {
    .intro-section,
    .theory-section,
    .viva-qa {
        box-shadow: none;
        border: 1px solid #000;
    }
    
    .viva-qa:hover {
        transform: none;
    }
}