/* ============================================
   CSS Variables (Theme)
   ============================================ */
:root {
    /* Colors */
    --bg: #ffffff;
    --surface: #ffffff;
    --text: #000000;
    --text-muted: #525252;
    --heading: #000000;
    
    /* Navigation */
    --nav-bg: #ffffff;
    --nav-link: #171717;
    --nav-link-scrolled: #171717;
    
    /* Primary */
    --primary: #2563eb;
    --primary-foreground: #ffffff;
    --primary-hover: #2159d4;
    --primary-active: #1f54c8;
    --primary-focus: #3f7dff;
    
    /* Secondary */
    --secondary: #ffffff;
    --secondary-foreground: #171717;
    --secondary-hover: #f5f5f5;
    
    /* Borders */
    --border: #e5e5e5;
    --border-muted: #ffffff;
    
    /* Status */
    --success: #10b981;
    --warning: #f59e0b;
    --danger: #ef4444;
    --danger-foreground: #ffffff;
    
    /* Spacing */
    --spacing-1: 0.25rem;
    --spacing-2: 0.5rem;
    --spacing-3: 0.75rem;
    --spacing-4: 1rem;
    --spacing-6: 1.5rem;
    --spacing-8: 2rem;
    --spacing-12: 3rem;
    --spacing-16: 4rem;
    --spacing-20: 5rem;
    --spacing-24: 6rem;
    
    /* Typography */
    --font-sans: 'Noto Sans KR', -apple-system, BlinkMacSystemFont, 'Segoe UI', sans-serif;
    --font-size-xs: 0.75rem;
    --font-size-sm: 0.875rem;
    --font-size-base: 1rem;
    --font-size-lg: 1.125rem;
    --font-size-xl: 1.25rem;
    --font-size-2xl: 1.5rem;
    --font-size-3xl: 1.875rem;
    --font-size-4xl: 2.25rem;
    --font-size-5xl: 3rem;
    --font-size-6xl: 3.75rem;
    
    /* Border Radius */
    --radius-sm: 0.125rem;
    --radius-base: 0.25rem;
    --radius-md: 0.375rem;
    --radius-lg: 0.5rem;
    --radius-xl: 0.75rem;
    --radius-2xl: 1rem;
    --radius-full: 9999px;
    
    /* Shadows */
    --shadow-sm: 0 1px 2px 0 rgb(0 0 0 / 0.05);
    --shadow-md: 0 4px 6px -1px rgb(0 0 0 / 0.1), 0 2px 4px -2px rgb(0 0 0 / 0.1);
    --shadow-lg: 0 10px 15px -3px rgb(0 0 0 / 0.1), 0 4px 6px -4px rgb(0 0 0 / 0.1);
    --shadow-xl: 0 20px 25px -5px rgb(0 0 0 / 0.1), 0 8px 10px -6px rgb(0 0 0 / 0.1);
    
    /* Transitions */
    --transition-fast: 0.15s ease;
    --transition-base: 0.3s ease;
    --transition-slow: 0.5s cubic-bezier(0.16, 1, 0.3, 1);
}

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

html {
    scroll-behavior: smooth;
    -webkit-overflow-scrolling: touch;
    overflow-x: hidden;
}

body {
    font-family: var(--font-sans);
    background-color: #ffffff;
    color: var(--text);
    overflow-x: hidden;
    -webkit-font-smoothing: antialiased;
    -moz-osx-font-smoothing: grayscale;
    line-height: 1.6;
    -webkit-font-smoothing: antialiased;
    -moz-osx-font-smoothing: grayscale;
}

.main-content {
    background-color: #ffffff;
    padding-top: var(--spacing-4);
    position: relative;
    z-index: 1;
}

/* ============================================
   Container
   ============================================ */
.container {
    width: 100%;
    max-width: 1280px;
    margin: 0 auto;
    padding: 0 var(--spacing-4);
}

@media (min-width: 768px) {
    .container {
        padding: 0 var(--spacing-6);
    }
}

/* ============================================
   Header
   ============================================ */
.main-header {
    position: fixed;
    top: 0;
    left: 0;
    right: 0;
    z-index: 50;
    background-color: rgba(255, 255, 255, 0.95);
    backdrop-filter: blur(8px);
    transition: all var(--transition-base);
    padding: var(--spacing-4) 0;
}

.main-header.scrolled {
    padding: var(--spacing-2) 0;
    box-shadow: var(--shadow-md);
    background-color: rgba(255, 255, 255, 0.9);
}

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

.logo {
    text-decoration: none;
    color: var(--text);
    transition: transform var(--transition-base);
}

.logo:hover {
    transform: scale(1.05);
}

.logo:active {
    transform: scale(0.95);
}

.logo-text {
    font-size: var(--font-size-xl);
    font-weight: 700;
    transition: font-size var(--transition-base);
}

.logo-image {
    height: 60px;
    width: auto;
    display: block;
    transition: height var(--transition-base);
    object-fit: contain;
}

.main-header.scrolled .logo-text {
    font-size: var(--font-size-lg);
}

.main-header.scrolled .logo-image {
    height: 48px;
}

.desktop-nav {
    display: none;
    align-items: center;
    gap: var(--spacing-6);
}

@media (min-width: 768px) {
    .desktop-nav {
        display: flex;
    }
}

.nav-link {
    font-size: calc(var(--font-size-sm) * 1.3);
    font-weight: 500;
    color: var(--nav-link);
    text-decoration: none;
    opacity: 0.8;
    transition: opacity var(--transition-base), background-color var(--transition-base);
    padding: 0.5rem 1rem;
    border-radius: 0.375rem;
}

.nav-link:hover {
    opacity: 1;
    background-color: #f5f5f5;
}

.desktop-actions {
    display: none;
    align-items: center;
    gap: var(--spacing-4);
}

.desktop-actions .btn {
    font-size: calc(var(--font-size-sm) * 1.1);
}

@media (min-width: 768px) {
    .desktop-actions {
        display: flex;
    }
}

.mobile-menu-toggle {
    display: flex;
    flex-direction: column;
    gap: 4px;
    background: none;
    border: none;
    cursor: pointer;
    padding: var(--spacing-2);
}

@media (min-width: 768px) {
    .mobile-menu-toggle {
        display: none;
    }
}

.menu-icon {
    width: 24px;
    height: 2px;
    background-color: var(--text);
    transition: all var(--transition-base);
}

.mobile-nav {
    display: none;
    flex-direction: column;
    gap: var(--spacing-4);
    padding: var(--spacing-4) 0;
    border-top: 1px solid var(--border);
    margin-top: var(--spacing-4);
}

.mobile-nav.active {
    display: flex;
}

.mobile-nav-link {
    font-size: var(--font-size-sm);
    font-weight: 500;
    color: var(--text);
    text-decoration: none;
    opacity: 0.8;
    transition: opacity var(--transition-base);
}

.mobile-nav-link:hover {
    opacity: 1;
}

.mobile-actions {
    display: flex;
    flex-direction: column;
    gap: var(--spacing-2);
    padding-top: var(--spacing-4);
    border-top: 1px solid var(--border);
    margin-top: var(--spacing-4);
}

/* Header Indicator */
.header-indicator {
    position: fixed;
    top: var(--spacing-6);
    left: 50%;
    transform: translateX(-50%);
    z-index: 60;
    pointer-events: none;
    opacity: 0;
    transition: opacity var(--transition-base);
}

.header-indicator.active {
    opacity: 1;
}

.header-indicator-content {
    padding: var(--spacing-3) var(--spacing-6);
    border-radius: var(--radius-full);
    box-shadow: var(--shadow-lg);
    backdrop-filter: blur(8px);
    font-size: var(--font-size-sm);
    font-weight: 500;
    text-transform: lowercase;
    min-width: 120px;
    text-align: center;
}

/* ============================================
   Hero Section
   ============================================ */
.hero-section {
    position: relative;
    width: 100%;
    aspect-ratio: 21 / 9;
    min-height: 400px;
    background-size: cover;
    background-position: center;
    background-repeat: no-repeat;
    display: flex;
    align-items: center;
    justify-content: center;
    margin-top: 80px;
}

.hero-overlay {
    position: absolute;
    inset: 0;
    background: linear-gradient(to bottom, rgba(0,0,0,0.3), rgba(0,0,0,0.5));
}

.hero-content {
    position: relative;
    z-index: 1;
    text-align: center;
    color: white;
    max-width: 800px;
    padding: var(--spacing-8);
}

.hero-title {
    font-size: var(--font-size-4xl);
    font-weight: 700;
    line-height: 1.2;
    margin-bottom: var(--spacing-6);
    text-shadow: 0 2px 4px rgba(0,0,0,0.3);
}

@media (min-width: 768px) {
    .hero-title {
        font-size: var(--font-size-5xl);
    }
}

@media (min-width: 1024px) {
    .hero-title {
        font-size: var(--font-size-6xl);
    }
}

.hero-description {
    font-size: var(--font-size-lg);
    line-height: 1.6;
    opacity: 0.95;
}

@media (min-width: 768px) {
    .hero-description {
        font-size: var(--font-size-xl);
    }
}

/* Page Hero (for other pages) */
.page-hero {
    position: relative;
    width: 100%;
    aspect-ratio: 21 / 9;
    min-height: 300px;
    background-size: cover;
    background-position: center;
    background-repeat: no-repeat;
    background-attachment: scroll;
    display: flex;
    align-items: center;
    justify-content: center;
    will-change: auto;
    transform: translate3d(0, 0, 0);
    -webkit-transform: translate3d(0, 0, 0);
    backface-visibility: hidden;
    -webkit-backface-visibility: hidden;
    perspective: 1000px;
    -webkit-perspective: 1000px;
    contain: layout style paint;
    z-index: 1;
}

.page-hero-overlay {
    position: absolute;
    inset: 0;
    background: linear-gradient(to bottom, rgba(0,0,0,0.2), rgba(0,0,0,0.4));
}

.page-hero-content {
    position: relative;
    z-index: 1;
    text-align: center;
    color: white;
    max-width: 800px;
    padding: var(--spacing-8);
}

.page-hero-title {
    font-size: var(--font-size-3xl);
    font-weight: 700;
    line-height: 1.2;
    margin-bottom: var(--spacing-4);
    text-shadow: 0 2px 4px rgba(0,0,0,0.3);
}

@media (min-width: 768px) {
    .page-hero-title {
        font-size: var(--font-size-4xl);
    }
}

@media (min-width: 1024px) {
    .page-hero-title {
        font-size: var(--font-size-5xl);
    }
}

/* ============================================
   Sections
   ============================================ */
.section {
    padding: var(--spacing-16) 0;
    margin-top: 0;
    position: relative;
    z-index: 1;
}

/* Section content alignment */
.section .container {
    text-align: center;
}

.section .container > * {
    text-align: center;
}

/* Allow left alignment for specific elements */
.section .container .card,
.section .container .form-group,
.section .container .course-list-container,
.section .container .timeline-container,
.section .container .post-list {
    text-align: left;
}

.section .container .card.text-center,
.section .container .form-group.text-center,
.section .container .hero-actions {
    text-align: center;
}

.hero-actions {
    display: flex;
    gap: 1rem;
    justify-content: center;
    flex-wrap: wrap;
}

@media (min-width: 768px) {
    .section {
        padding: var(--spacing-20) 0;
    }
}

.section-title {
    font-size: var(--font-size-3xl);
    font-weight: 700;
    line-height: 1.2;
    margin-bottom: var(--spacing-6);
    text-align: center;
}

@media (min-width: 768px) {
    .section-title {
        font-size: var(--font-size-4xl);
    }
}

@media (min-width: 1024px) {
    .section-title {
        font-size: var(--font-size-5xl);
    }
}

.section-description {
    font-size: var(--font-size-lg);
    color: var(--text-muted);
    line-height: 1.6;
    text-align: center;
}

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

/* ============================================
   Buttons
   ============================================ */
.btn {
    display: inline-flex;
    align-items: center;
    justify-content: center;
    padding: var(--spacing-2) var(--spacing-4);
    font-size: var(--font-size-sm);
    font-weight: 500;
    border-radius: var(--radius-lg);
    border: none;
    cursor: pointer;
    text-decoration: none;
    transition: all var(--transition-base);
    line-height: 1.5;
}

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

.btn-primary:hover {
    background-color: var(--primary-hover);
    transform: scale(1.02);
}

.btn-primary:active {
    transform: scale(0.98);
}

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

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

.btn-ghost {
    background-color: transparent;
    color: var(--text);
}

.btn-ghost:hover {
    background-color: rgba(0, 0, 0, 0.05);
}

.btn-sm {
    padding: var(--spacing-1.5) var(--spacing-3);
    font-size: var(--font-size-xs);
}

.btn-lg {
    padding: var(--spacing-3) var(--spacing-6);
    font-size: var(--font-size-base);
}

.btn-block {
    width: 100%;
}

/* ============================================
   Course Grid
   ============================================ */
.course-grid {
    display: grid;
    grid-template-columns: 1fr;
    gap: var(--spacing-6);
    margin-top: var(--spacing-12);
}

@media (min-width: 768px) {
    .course-grid {
        grid-template-columns: repeat(2, 1fr);
    }
}

@media (min-width: 1024px) {
    .course-grid {
        grid-template-columns: repeat(3, 1fr);
    }
}

@media (min-width: 1280px) {
    .course-grid {
        grid-template-columns: repeat(4, 1fr);
    }
}

.grid-item {
    position: relative;
    background-color: var(--surface);
    border-radius: var(--radius-2xl);
    padding: var(--spacing-8);
    min-height: 320px;
    border: 1px solid #e5e5e5;
    cursor: pointer;
    transition: all var(--transition-slow);
    box-shadow: var(--shadow-sm);
    overflow: hidden;
}

.grid-item:hover {
    transform: translateY(-8px) scale(0.98);
    box-shadow: var(--shadow-xl);
}

.grid-item-overlay {
    position: absolute;
    inset: 0;
    opacity: 0;
    transition: opacity var(--transition-slow);
    pointer-events: none;
}

.grid-item:hover .grid-item-overlay {
    opacity: 0.1;
}

.grid-item-content {
    position: relative;
    z-index: 1;
    display: flex;
    flex-direction: column;
    align-items: center;
    text-align: center;
    gap: var(--spacing-4);
}

.grid-item-icon {
    width: 64px;
    height: 64px;
    border-radius: var(--radius-full);
    display: flex;
    align-items: center;
    justify-content: center;
    color: white;
    font-weight: 700;
    font-size: calc(var(--font-size-sm) * 1.5);
    box-shadow: inset 0 2px 4px rgba(0,0,0,0.2);
    margin-bottom: var(--spacing-2);
}

.grid-item-title {
    font-size: var(--font-size-xl);
    font-weight: 700;
    color: var(--heading);
    line-height: 1.3;
    display: -webkit-box;
    -webkit-line-clamp: 2;
    -webkit-box-orient: vertical;
    overflow: hidden;
}

.grid-item-description {
    font-size: var(--font-size-sm);
    color: var(--text-muted);
    font-weight: 500;
    line-height: 1.5;
    display: -webkit-box;
    -webkit-line-clamp: 3;
    -webkit-box-orient: vertical;
    overflow: hidden;
}

/* ============================================
   Cards
   ============================================ */
.card {
    background-color: var(--surface);
    border-radius: var(--radius-lg);
    padding: var(--spacing-6);
    box-shadow: var(--shadow-md);
    transition: all var(--transition-slow);
}

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

.card-header {
    margin-bottom: var(--spacing-4);
}

.card-title {
    font-size: var(--font-size-xl);
    font-weight: 700;
    margin-bottom: var(--spacing-2);
}

.card-description {
    font-size: var(--font-size-base);
    color: var(--text-muted);
    line-height: 1.6;
}

/* ============================================
   Footer
   ============================================ */
.main-footer {
    background-color: #ffffff;
    border-top: 1px solid var(--border);
    padding: var(--spacing-12) 0;
    margin-top: var(--spacing-16);
}

.footer-cta {
    text-align: center;
    margin-bottom: var(--spacing-12);
}

.footer-cta-title {
    font-size: var(--font-size-2xl);
    font-weight: 700;
    margin-bottom: var(--spacing-4);
}

@media (min-width: 768px) {
    .footer-cta-title {
        font-size: var(--font-size-3xl);
    }
}

.footer-cta-description {
    color: var(--text-muted);
    margin-bottom: var(--spacing-6);
    max-width: 600px;
    margin-left: auto;
    margin-right: auto;
}

.footer-cta-buttons {
    display: flex;
    flex-direction: column;
    gap: var(--spacing-4);
    align-items: center;
    justify-content: center;
}

@media (min-width: 640px) {
    .footer-cta-buttons {
        flex-direction: row;
    }
}

.footer-links {
    display: grid;
    grid-template-columns: repeat(2, 1fr);
    gap: var(--spacing-8);
    margin-bottom: var(--spacing-8);
}

@media (min-width: 768px) {
    .footer-links {
        grid-template-columns: repeat(4, 1fr);
    }
}

.footer-link-title {
    font-size: var(--font-size-sm);
    font-weight: 600;
    margin-bottom: var(--spacing-4);
}

.footer-link-list {
    list-style: none;
    display: flex;
    flex-direction: column;
    gap: var(--spacing-2);
}

.footer-link-list a {
    font-size: var(--font-size-sm);
    color: var(--text-muted);
    text-decoration: none;
    transition: color var(--transition-base);
}

.footer-link-list a:hover {
    color: var(--text);
}

.footer-bottom {
    display: flex;
    flex-direction: column;
    justify-content: space-between;
    align-items: center;
    gap: var(--spacing-4);
    padding-top: var(--spacing-8);
    border-top: 1px solid var(--border);
}

@media (min-width: 768px) {
    .footer-bottom {
        flex-direction: row;
        align-items: center;
    }
}

.footer-copyright {
    font-size: var(--font-size-sm);
    color: var(--text-muted);
    line-height: 1.5;
    display: flex;
    align-items: center;
    margin: 0;
    height: auto;
}

.footer-contact {
    display: flex;
    align-items: center;
    margin: 0;
    height: auto;
}

.footer-legal {
    display: flex;
    align-items: center;
    gap: var(--spacing-6);
    margin: 0;
    height: auto;
}

.footer-legal a {
    font-size: var(--font-size-sm);
    color: var(--text-muted);
    text-decoration: none;
    transition: color var(--transition-base);
}

.footer-legal a:hover {
    color: var(--text);
}

/* ============================================
   Utility Classes
   ============================================ */
.hidden-sm {
    display: none;
}

@media (min-width: 640px) {
    .hidden-sm {
        display: block;
    }
}

.gradient-text {
    background: linear-gradient(135deg, var(--heading) 0%, var(--text-muted) 100%);
    -webkit-background-clip: text;
    -webkit-text-fill-color: transparent;
    background-clip: text;
}

/* ============================================
   Forms
   ============================================ */
.form-group {
    margin-bottom: var(--spacing-4);
}

.form-label {
    display: block;
    font-size: var(--font-size-sm);
    font-weight: 500;
    margin-bottom: var(--spacing-2);
    color: var(--text);
}

.form-input {
    width: 100%;
    padding: var(--spacing-2) var(--spacing-3);
    font-size: var(--font-size-base);
    border: 1px solid var(--border);
    border-radius: var(--radius-lg);
    transition: all var(--transition-base);
    font-family: var(--font-sans);
}

.form-input:focus {
    outline: none;
    border-color: var(--primary);
    box-shadow: 0 0 0 3px rgba(37, 99, 235, 0.1);
}

.form-input.error {
    border-color: var(--danger);
}

.form-error {
    font-size: var(--font-size-sm);
    color: var(--danger);
    margin-top: var(--spacing-1);
}

/* ============================================
   Additional Styles
   ============================================ */
.hero-actions {
    display: flex;
    flex-direction: column;
    gap: 1rem;
    align-items: center;
    justify-content: center;
}

@media (min-width: 640px) {
    .hero-actions {
        flex-direction: row;
    }
}

/* ============================================
   Responsive
   ============================================ */
@media (max-width: 767px) {
    .hero-title {
        font-size: var(--font-size-3xl);
    }
    
    .section-title {
        font-size: var(--font-size-2xl);
    }
    
    .grid-item {
        min-height: 280px;
    }
}