:root {
    /* Modern Color Palette */
    --primary-blue: #4F46E5;
    --primary-indigo: #6366F1;
    --primary-purple: #8B5CF6;
    --primary-pink: #EC4899;
    --primary-teal: #14B8A6;
    --primary-cyan: #06B6D4;
    --primary-green: #10B981;
    --primary-yellow: #F59E0B;
    --primary-orange: #F97316;
    --primary-red: #EF4444;
    
    /* Gradients */
    --gradient-primary: linear-gradient(135deg, var(--primary-indigo) 0%, var(--primary-cyan) 100%);
    --gradient-secondary: linear-gradient(135deg, var(--primary-purple) 0%, var(--primary-pink) 100%);
    --gradient-warning: linear-gradient(135deg, var(--primary-orange) 0%, var(--primary-yellow) 100%);
    --gradient-success: linear-gradient(135deg, var(--primary-teal) 0%, var(--primary-green) 100%);
    
    /* Neutral Colors */
    --gray-50: #F9FAFB;
    --gray-100: #F3F4F6;
    --gray-200: #E5E7EB;
    --gray-300: #D1D5DB;
    --gray-400: #9CA3AF;
    --gray-500: #6B7280;
    --gray-600: #4B5563;
    --gray-700: #374151;
    --gray-800: #1F2937;
    --gray-900: #111827;
    
    /* Functional Colors */
    --success-color: #10B981;
    --warning-color: #F59E0B;
    --danger-color: #EF4444;
    --info-color: #3B82F6;
    
    /* Typography */
    --font-heading: 'Poppins', sans-serif;
    --font-body: 'Inter', sans-serif;
    --font-accent: 'Nunito', sans-serif;
    
    /* Spacing */
    --spacing-xs: 0.5rem;
    --spacing-sm: 1rem;
    --spacing-md: 1.5rem;
    --spacing-lg: 2rem;
    --spacing-xl: 3rem;
    --spacing-xxl: 5rem;
    
    /* Border Radius */
    --radius-sm: 0.5rem;
    --radius-md: 0.75rem;
    --radius-lg: 1rem;
    --radius-xl: 1.5rem;
    --radius-round: 50%;
    
    /* Shadows */
    --shadow-sm: 0 1px 3px rgba(0, 0, 0, 0.1);
    --shadow-md: 0 4px 6px -1px rgba(0, 0, 0, 0.1), 0 2px 4px -1px rgba(0, 0, 0, 0.06);
    --shadow-lg: 0 10px 15px -3px rgba(0, 0, 0, 0.1), 0 4px 6px -2px rgba(0, 0, 0, 0.05);
    --shadow-xl: 0 20px 25px -5px rgba(0, 0, 0, 0.1), 0 10px 10px -5px rgba(0, 0, 0, 0.04);
    --shadow-2xl: 0 25px 50px -12px rgba(0, 0, 0, 0.25);
    
    /* Transitions */
    --transition-fast: 0.2s cubic-bezier(0.4, 0, 0.2, 1);
    --transition-medium: 0.3s cubic-bezier(0.4, 0, 0.2, 1);
    --transition-slow: 0.5s cubic-bezier(0.4, 0, 0.2, 1);
    
    /* Container */
    --container-width: 1200px;
}

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

html {
    scroll-behavior: smooth;
    font-size: 16px;
}

body {
    font-family: var(--font-body);
    font-size: 1rem;
    line-height: 1.6;
    color: var(--gray-700);
    background-color: var(--gray-50);
    overflow-x: hidden;
}

h1, h2, h3, h4, h5, h6 {
    font-family: var(--font-heading);
    font-weight: 600;
    line-height: 1.3;
    color: var(--gray-900);
}

h1 {
    font-size: 3.5rem;
    font-weight: 800;
}

h2 {
    font-size: 2.5rem;
}

h3 {
    font-size: 1.75rem;
}

h4 {
    font-size: 1.5rem;
}

p {
    margin-bottom: var(--spacing-md);
    color: var(--gray-600);
}

a {
    text-decoration: none;
    color: inherit;
    transition: var(--transition-fast);
}

ul, ol {
    list-style: none;
}

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

/* Container */
.container {
    width: 100%;
    max-width: var(--container-width);
    margin: 0 auto;
    padding: 0 var(--spacing-md);
}

/* Preloader */
.preloader {
    position: fixed;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    background: var(--gradient-primary);
    display: flex;
    align-items: center;
    justify-content: center;
    z-index: 9999;
    transition: opacity 0.5s ease, visibility 0.5s ease;
}

.preloader-content {
    text-align: center;
    color: white;
}

.preloader-spinner {
    width: 60px;
    height: 60px;
    border: 4px solid rgba(255, 255, 255, 0.3);
    border-radius: var(--radius-round);
    border-top-color: white;
    animation: spin 1s linear infinite;
    margin: 0 auto var(--spacing-md);
}

@keyframes spin {
    0% { transform: rotate(0deg); }
    100% { transform: rotate(360deg); }
}

.preloader-text {
    font-size: 1.25rem;
    font-weight: 600;
    color: white;
}

/* Header */
.main-header {
    background-color: white;
    box-shadow: var(--shadow-md);
    position: sticky;
    top: 0;
    z-index: 100;
    transition: var(--transition-medium);
}

.main-header.scrolled {
    box-shadow: var(--shadow-lg);
}

.header-container {
    display: flex;
    justify-content: space-between;
    align-items: center;
    padding: var(--spacing-sm) 0;
}

.logo {
    display: flex;
    align-items: center;
    gap: var(--spacing-sm);
}

.logo i {
    font-size: 2rem;
    color: var(--primary-indigo);
}

.logo-text {
    display: flex;
    flex-direction: column;
}

.site-name {
    font-size: 1.75rem;
    font-weight: 800;
    color: var(--primary-indigo);
    margin: 0;
    line-height: 1;
}

.logo-tagline {
    font-size: 0.75rem;
    color: var(--gray-500);
    margin: 0;
    font-weight: 500;
    letter-spacing: 0.5px;
}

/* Navigation */
.nav-list {
    display: flex;
    gap: var(--spacing-lg);
}

.nav-link {
    font-weight: 600;
    color: var(--gray-600);
    padding: var(--spacing-xs) 0;
    position: relative;
    transition: var(--transition-fast);
}

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

.nav-link::after {
    content: '';
    position: absolute;
    bottom: 0;
    left: 0;
    width: 0;
    height: 3px;
    background: var(--gradient-primary);
    border-radius: 2px;
    transition: var(--transition-medium);
}

.nav-link:hover::after,
.nav-link.active::after {
    width: 100%;
}

/* Header Actions */
.header-actions {
    display: flex;
    align-items: center;
    gap: var(--spacing-md);
}

/* Language Selector */
.language-selector {
    position: relative;
}

.language-dropdown {
    appearance: none;
    background-color: white;
    border: 2px solid var(--gray-200);
    border-radius: var(--radius-sm);
    padding: 0.5rem 2rem 0.5rem 0.75rem;
    font-size: 0.875rem;
    font-weight: 600;
    color: var(--gray-700);
    cursor: pointer;
    background-image: url("data:image/svg+xml,%3Csvg xmlns='http://www.w3.org/2000/svg' width='16' height='16' fill='%236366F1' viewBox='0 0 16 16'%3E%3Cpath d='M7.247 11.14 2.451 5.658C1.885 5.013 2.345 4 3.204 4h9.592a1 1 0 0 1 .753 1.659l-4.796 5.48a1 1 0 0 1-1.506 0z'/%3E%3C/svg%3E");
    background-repeat: no-repeat;
    background-position: right 0.75rem center;
    background-size: 12px;
    transition: var(--transition-fast);
}

.language-dropdown:hover,
.language-dropdown:focus {
    border-color: var(--primary-indigo);
    outline: none;
    box-shadow: 0 0 0 3px rgba(99, 102, 241, 0.1);
}

/* Buttons */
.btn {
    display: inline-flex;
    align-items: center;
    justify-content: center;
    padding: 0.75rem 1.5rem;
    border-radius: var(--radius-sm);
    font-weight: 600;
    font-size: 1rem;
    cursor: pointer;
    border: 2px solid transparent;
    transition: var(--transition-medium);
    gap: 0.5rem;
    white-space: nowrap;
}

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

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

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

.btn-secondary:hover {
    background-color: var(--primary-indigo);
    color: white;
    transform: translateY(-2px);
}

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

.btn-outline:hover {
    background-color: var(--primary-indigo);
    color: white;
    transform: translateY(-2px);
}

.btn-small {
    padding: 0.5rem 1rem;
    font-size: 0.875rem;
}

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

.btn-block {
    display: block;
    width: 100%;
}

/* Mobile Menu */
.mobile-menu-btn {
    display: none;
    background: none;
    border: none;
    font-size: 1.5rem;
    color: var(--gray-700);
    cursor: pointer;
    padding: var(--spacing-xs);
}

/* Page Sections */
.page {
    display: none;
    animation: fadeIn 0.5s ease;
}

.page.active {
    display: block;
}

@keyframes fadeIn {
    from { opacity: 0; transform: translateY(20px); }
    to { opacity: 1; transform: translateY(0); }
}

/* Section Header */
.section-header {
    text-align: center;
    margin-bottom: var(--spacing-xl);
}

.section-label {
    display: inline-block;
    padding: 0.25rem 1rem;
    background: var(--gradient-primary);
    color: white;
    border-radius: 2rem;
    font-size: 0.875rem;
    font-weight: 600;
    margin-bottom: var(--spacing-md);
}

.section-title {
    margin-bottom: var(--spacing-md);
    color: var(--gray-900);
}

.section-subtitle {
    max-width: 700px;
    margin: 0 auto;
    color: var(--gray-600);
    font-size: 1.125rem;
}

/* Features Section */
.features-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(280px, 1fr));
    gap: var(--spacing-lg);
    margin-top: var(--spacing-xl);
}

.feature-card {
    background-color: white;
    border-radius: var(--radius-lg);
    padding: var(--spacing-lg);
    box-shadow: var(--shadow-md);
    transition: var(--transition-medium);
    border: 1px solid transparent;
}

.feature-card:hover {
    transform: translateY(-10px);
    border-color: var(--primary-indigo);
    box-shadow: var(--shadow-xl);
}

.feature-icon {
    margin-bottom: var(--spacing-md);
}

.icon-wrapper {
    width: 70px;
    height: 70px;
    background: var(--gradient-primary);
    border-radius: var(--radius-md);
    display: flex;
    align-items: center;
    justify-content: center;
    color: white;
    font-size: 1.75rem;
}

.feature-card h3 {
    margin-bottom: var(--spacing-sm);
    color: var(--gray-900);
}

.feature-list {
    margin-top: var(--spacing-md);
}

.feature-list li {
    display: flex;
    align-items: center;
    gap: var(--spacing-sm);
    margin-bottom: 0.5rem;
    color: var(--gray-600);
}

.feature-list i {
    color: var(--primary-green);
}

/* Stats Section */
.stats-section {
    background: var(--gradient-primary);
    color: white;
    padding: var(--spacing-xl) 0;
}

.stats-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(200px, 1fr));
    gap: var(--spacing-lg);
}

.stat-card {
    display: flex;
    align-items: center;
    gap: var(--spacing-md);
    padding: var(--spacing-lg);
    background: rgba(255, 255, 255, 0.1);
    border-radius: var(--radius-lg);
    backdrop-filter: blur(10px);
}

.stat-icon {
    width: 60px;
    height: 60px;
    background: rgba(255, 255, 255, 0.2);
    border-radius: var(--radius-round);
    display: flex;
    align-items: center;
    justify-content: center;
    font-size: 1.5rem;
}

.stat-content {
    display: flex;
    flex-direction: column;
}

.stat-number {
    font-size: 2.5rem;
    font-weight: 800;
    font-family: var(--font-heading);
    line-height: 1;
}

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

/* CTA Section */
.cta-section {
    background: linear-gradient(135deg, var(--gray-900) 0%, var(--gray-800) 100%);
    color: white;
    padding: var(--spacing-xl) 0;
    text-align: center;
}

.cta-title {
    color: white;
    margin-bottom: var(--spacing-sm);
}

.cta-subtitle {
    color: var(--gray-300);
    margin-bottom: var(--spacing-lg);
    font-size: 1.125rem;
}

.cta-buttons {
    display: flex;
    justify-content: center;
    gap: var(--spacing-md);
    flex-wrap: wrap;
}

/* Form Styles */
.form-row {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(250px, 1fr));
    gap: var(--spacing-lg);
    margin-bottom: var(--spacing-lg);
}

.form-group {
    margin-bottom: var(--spacing-md);
}

.form-group label {
    display: flex;
    align-items: center;
    gap: 0.5rem;
    margin-bottom: 0.5rem;
    font-weight: 600;
    color: var(--gray-700);
}

.form-control {
    width: 100%;
    padding: 0.875rem 1rem;
    border: 2px solid var(--gray-200);
    border-radius: var(--radius-sm);
    font-family: var(--font-body);
    font-size: 1rem;
    transition: var(--transition-fast);
    background-color: white;
}

.form-control:focus {
    outline: none;
    border-color: var(--primary-indigo);
    box-shadow: 0 0 0 3px rgba(99, 102, 241, 0.1);
}

textarea.form-control {
    resize: vertical;
    min-height: 100px;
}

/* Difficulty Selector */
.difficulty-selector {
    display: flex;
    gap: var(--spacing-sm);
}

.difficulty-option {
    flex: 1;
    text-align: center;
}

.difficulty-option input {
    display: none;
}

.difficulty-label {
    display: block;
    padding: 0.75rem;
    background-color: var(--gray-100);
    border: 2px solid var(--gray-200);
    border-radius: var(--radius-sm);
    font-weight: 600;
    cursor: pointer;
    transition: var(--transition-fast);
}

.difficulty-option input:checked + .difficulty-label {
    background-color: var(--primary-indigo);
    color: white;
    border-color: var(--primary-indigo);
}

.difficulty-label.beginner {
    border-color: var(--primary-green);
    color: var(--primary-green);
}

.difficulty-label.intermediate {
    border-color: var(--primary-yellow);
    color: var(--primary-yellow);
}

.difficulty-label.advanced {
    border-color: var(--primary-red);
    color: var(--primary-red);
}

.difficulty-option input:checked + .difficulty-label.beginner {
    background-color: var(--primary-green);
    color: white;
}

.difficulty-option input:checked + .difficulty-label.intermediate {
    background-color: var(--primary-yellow);
    color: white;
}

.difficulty-option input:checked + .difficulty-label.advanced {
    background-color: var(--primary-red);
    color: white;
}

/* Form Actions */
.form-actions {
    display: flex;
    justify-content: flex-end;
    gap: var(--spacing-md);
    margin-top: var(--spacing-lg);
}

/* Footer */
.main-footer {
    background-color: var(--gray-900);
    color: white;
    padding-top: var(--spacing-xl);
}

.footer-content {
    display: grid;
    grid-template-columns: 1fr 2fr;
    gap: var(--spacing-xl);
    margin-bottom: var(--spacing-xl);
}

.footer-brand {
    max-width: 300px;
}

.footer-logo {
    display: flex;
    align-items: center;
    gap: var(--spacing-sm);
    margin-bottom: var(--spacing-md);
}

.footer-logo i {
    font-size: 2rem;
    color: var(--primary-cyan);
}

.footer-logo h3 {
    font-size: 1.75rem;
    color: white;
    margin: 0;
}

.footer-tagline {
    color: var(--gray-400);
    margin-bottom: var(--spacing-md);
}

.footer-social {
    display: flex;
    gap: var(--spacing-sm);
}

.social-link {
    width: 40px;
    height: 40px;
    background-color: rgba(255, 255, 255, 0.1);
    border-radius: var(--radius-round);
    display: flex;
    align-items: center;
    justify-content: center;
    color: white;
    transition: var(--transition-fast);
}

.social-link:hover {
    background-color: var(--primary-indigo);
    transform: translateY(-2px);
}

.footer-links {
    display: grid;
    grid-template-columns: repeat(4, 1fr);
    gap: var(--spacing-lg);
}

.footer-column h4 {
    color: white;
    margin-bottom: var(--spacing-md);
    font-size: 1.125rem;
}

.footer-column ul {
    display: flex;
    flex-direction: column;
    gap: 0.75rem;
}

.footer-column a {
    color: var(--gray-400);
    font-size: 0.875rem;
}

.footer-column a:hover {
    color: white;
    padding-left: 5px;
}

.footer-bottom {
    border-top: 1px solid rgba(255, 255, 255, 0.1);
    padding: var(--spacing-lg) 0;
}

.footer-bottom-content {
    display: flex;
    justify-content: space-between;
    align-items: center;
    flex-wrap: wrap;
    gap: var(--spacing-md);
}

.footer-bottom p {
    color: var(--gray-400);
    margin: 0;
    font-size: 0.875rem;
}

.footer-legal {
    display: flex;
    gap: var(--spacing-lg);
}

.footer-legal a {
    color: var(--gray-400);
    font-size: 0.875rem;
}

.footer-legal a:hover {
    color: white;
}

/* Chat Widget */
.chat-widget {
    position: fixed;
    bottom: var(--spacing-lg);
    right: var(--spacing-lg);
    z-index: 1000;
}

.chat-toggle {
    width: 60px;
    height: 60px;
    background: var(--gradient-primary);
    border: none;
    border-radius: var(--radius-round);
    color: white;
    font-size: 1.5rem;
    cursor: pointer;
    box-shadow: var(--shadow-xl);
    transition: var(--transition-medium);
}

.chat-toggle:hover {
    transform: scale(1.1);
}

.chat-container {
    position: absolute;
    bottom: 70px;
    right: 0;
    width: 350px;
    background: white;
    border-radius: var(--radius-lg);
    box-shadow: var(--shadow-2xl);
    display: none;
    overflow: hidden;
}

.chat-container.open {
    display: block;
    animation: slideUp 0.3s ease;
}

@keyframes slideUp {
    from { transform: translateY(20px); opacity: 0; }
    to { transform: translateY(0); opacity: 1; }
}

.chat-header {
    background: var(--gradient-primary);
    color: white;
    padding: var(--spacing-md);
    display: flex;
    justify-content: space-between;
    align-items: center;
}

.chat-header h4 {
    color: white;
    margin: 0;
    font-size: 1.125rem;
}

.chat-close {
    background: none;
    border: none;
    color: white;
    font-size: 1.25rem;
    cursor: pointer;
    padding: 0;
}

.chat-body {
    height: 300px;
    padding: var(--spacing-md);
    overflow-y: auto;
}

.chat-message {
    margin-bottom: var(--spacing-sm);
    display: flex;
}

.chat-message.bot {
    justify-content: flex-start;
}

.chat-message.user {
    justify-content: flex-end;
}

.message-content {
    max-width: 80%;
    padding: 0.75rem 1rem;
    border-radius: var(--radius-md);
    font-size: 0.875rem;
    line-height: 1.4;
}

.chat-message.bot .message-content {
    background-color: var(--gray-100);
    color: var(--gray-700);
}

.chat-message.user .message-content {
    background: var(--gradient-primary);
    color: white;
}

.chat-input {
    display: flex;
    padding: var(--spacing-md);
    border-top: 1px solid var(--gray-200);
    gap: var(--spacing-sm);
}

.chat-input input {
    flex: 1;
    padding: 0.75rem;
    border: 2px solid var(--gray-200);
    border-radius: var(--radius-sm);
    font-family: var(--font-body);
    font-size: 0.875rem;
}

.chat-input input:focus {
    outline: none;
    border-color: var(--primary-indigo);
}

.chat-send {
    width: 45px;
    height: 45px;
    background: var(--gradient-primary);
    border: none;
    border-radius: var(--radius-sm);
    color: white;
    cursor: pointer;
    transition: var(--transition-fast);
}

.chat-send:hover {
    transform: scale(1.05);
}

/* Back to Top Button */
.back-to-top {
    position: fixed;
    bottom: var(--spacing-lg);
    left: var(--spacing-lg);
    width: 50px;
    height: 50px;
    background: var(--gradient-primary);
    border: none;
    border-radius: var(--radius-round);
    color: white;
    font-size: 1.25rem;
    cursor: pointer;
    box-shadow: var(--shadow-lg);
    z-index: 999;
    opacity: 0;
    visibility: hidden;
    transition: var(--transition-medium);
}

.back-to-top.visible {
    opacity: 1;
    visibility: visible;
}

.back-to-top:hover {
    transform: translateY(-5px);
    box-shadow: var(--shadow-xl);
}

/* Responsive Design */
@media (max-width: 1200px) {
    .footer-content {
        grid-template-columns: 1fr;
        gap: var(--spacing-xl);
    }
    
    .footer-links {
        grid-template-columns: repeat(2, 1fr);
    }
}

@media (max-width: 992px) {
    h1 { font-size: 2.75rem; }
    h2 { font-size: 2.25rem; }
    
    .main-nav {
        position: fixed;
        top: 70px;
        left: 0;
        width: 100%;
        background: white;
        box-shadow: var(--shadow-lg);
        padding: var(--spacing-lg);
        transform: translateY(-100%);
        opacity: 0;
        visibility: hidden;
        transition: var(--transition-medium);
    }
    
    .main-nav.open {
        transform: translateY(0);
        opacity: 1;
        visibility: visible;
    }
    
    .nav-list {
        flex-direction: column;
        gap: 0;
    }
    
    .nav-item {
        width: 100%;
    }
    
    .nav-link {
        display: block;
        padding: var(--spacing-md);
        border-bottom: 1px solid var(--gray-100);
    }
    
    .nav-link::after {
        display: none;
    }
    
    .mobile-menu-btn {
        display: block;
    }
    
    .header-actions {
        display: none;
    }
    
    .footer-content {
        grid-template-columns: 1fr;
    }
    
    .footer-links {
        grid-template-columns: 1fr;
    }
}

@media (max-width: 768px) {
    h1 { font-size: 2.25rem; }
    h2 { font-size: 1.875rem; }
    h3 { font-size: 1.5rem; }
    
    .stats-grid {
        grid-template-columns: repeat(2, 1fr);
    }
    
    .features-grid {
        grid-template-columns: 1fr;
    }
    
    .form-row {
        grid-template-columns: 1fr;
    }
    
    .form-actions {
        flex-direction: column;
    }
    
    .form-actions .btn {
        width: 100%;
    }
    
    .chat-container {
        width: calc(100vw - 40px);
        right: 20px;
    }
    
    .footer-bottom-content {
        flex-direction: column;
        text-align: center;
        gap: var(--spacing-sm);
    }
}

@media (max-width: 576px) {
    .container {
        padding: 0 var(--spacing-sm);
    }
    
    .hero-cta {
        flex-direction: column;
        width: 100%;
    }
    
    .hero-cta .btn {
        width: 100%;
    }
    
    .cta-buttons {
        flex-direction: column;
    }
    
    .cta-buttons .btn {
        width: 100%;
    }
    
    .stats-grid {
        grid-template-columns: 1fr;
    }
    
    .difficulty-selector {
        flex-direction: column;
    }
}