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

:root {
    --primary-color: #6366f1;
    --primary-hover: #4f46e5;
    --text-color: #1f2937;
    --text-light: #6b7280;
    --bg-color: #ffffff;
    --bg-light: #f9fafb;
    --border-color: #e5e7eb;
    --shadow: 0 1px 3px 0 rgba(0, 0, 0, 0.1), 0 1px 2px 0 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);
}

body {
    font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, 'Helvetica Neue', Arial, sans-serif;
    color: var(--text-color);
    background-color: var(--bg-light);
    line-height: 1.6;
}

.container {
    max-width: 1200px;
    margin: 0 auto;
    padding: 0 20px;
}

/* Header */
.header {
    background-color: var(--bg-color);
    border-bottom: 1px solid var(--border-color);
    padding: 1rem 0;
    position: sticky;
    top: 0;
    z-index: 100;
    box-shadow: var(--shadow);
}

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

h1.logo,
.logo {
    display: flex;
    align-items: center;
    height: 2.376rem;
    margin: 0;
    padding: 0;
    font-size: 0;
    line-height: 2.376rem;
    font-weight: normal;
}

h1.logo img,
.logo img {
    max-height: 2.376rem !important;
    height: 2.376rem !important;
    width: auto !important;
    max-width: 317px !important;
    object-fit: contain;
    display: block;
    margin: 0;
    padding: 0;
}

h1.logo a,
.logo a {
    text-decoration: none;
    color: inherit;
    display: inline-flex;
    align-items: center;
    height: 2.376rem;
    margin: 0;
    padding: 0;
}

h1.logo a img,
.logo a img {
    max-height: 2.376rem !important;
    height: 2.376rem !important;
    width: auto !important;
    max-width: 317px !important;
    object-fit: contain;
    margin: 0;
    padding: 0;
}

.nav {
    display: flex;
    gap: 1.5rem;
}

.nav a {
    text-decoration: none;
    color: var(--text-color);
    font-weight: 500;
    transition: color 0.2s;
}

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

/* Main */
.main {
    min-height: calc(100vh - 200px);
    padding: 2rem 0;
}

/* Hero Section */
.hero {
    text-align: center;
    padding: 3rem 0;
    margin-bottom: 3rem;
}

.hero h2 {
    font-size: 2.5rem;
    margin-bottom: 1rem;
    color: var(--text-color);
}

.hero p {
    font-size: 1.25rem;
    color: var(--text-light);
    margin-bottom: 0.5rem;
}

.hero .subtitle {
    font-size: 1rem;
}

/* Categories */
.categories {
    margin-bottom: 2rem;
}

.category-filter {
    display: flex;
    flex-wrap: wrap;
    gap: 0.5rem;
}

.category-btn {
    padding: 0.5rem 1rem;
    background-color: var(--bg-color);
    border: 1px solid var(--border-color);
    border-radius: 0.5rem;
    text-decoration: none;
    color: var(--text-color);
    font-weight: 500;
    transition: all 0.2s;
}

.category-btn:hover {
    border-color: var(--primary-color);
    color: var(--primary-color);
}

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

/* Courses Section */
.section-title {
    font-size: 1.75rem;
    margin-bottom: 1.5rem;
    color: var(--text-color);
}

.courses-grid {
    display: grid;
    grid-template-columns: repeat(auto-fill, minmax(300px, 1fr));
    gap: 1.5rem;
    margin-bottom: 2rem;
}

.course-card {
    background-color: var(--bg-color);
    border-radius: 0.75rem;
    overflow: hidden;
    box-shadow: var(--shadow);
    transition: transform 0.2s, box-shadow 0.2s;
}

.course-card:hover {
    transform: translateY(-4px);
    box-shadow: var(--shadow-lg);
}

.course-card a {
    text-decoration: none;
    color: inherit;
    display: block;
}

.course-thumbnail {
    position: relative;
    width: 100%;
    padding-top: 56.25%; /* 16:9 aspect ratio */
    background-color: #000;
    overflow: hidden;
}

.course-thumbnail img {
    position: absolute;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    object-fit: cover;
}

.play-overlay {
    position: absolute;
    top: 50%;
    left: 50%;
    transform: translate(-50%, -50%);
    opacity: 0.9;
    transition: opacity 0.2s;
}

.course-card:hover .play-overlay {
    opacity: 1;
}

.course-info {
    padding: 1rem;
}

.course-title {
    font-size: 1.1rem;
    font-weight: 600;
    margin-bottom: 0.5rem;
    color: var(--text-color);
    display: -webkit-box;
    -webkit-line-clamp: 2;
    -webkit-box-orient: vertical;
    overflow: hidden;
}

.course-category {
    display: inline-block;
    padding: 0.25rem 0.5rem;
    background-color: var(--bg-light);
    border-radius: 0.25rem;
    font-size: 0.875rem;
    color: var(--text-light);
    margin-bottom: 0.5rem;
}

.course-description {
    font-size: 0.875rem;
    color: var(--text-light);
    margin-bottom: 0.5rem;
    display: -webkit-box;
    -webkit-line-clamp: 2;
    -webkit-box-orient: vertical;
    overflow: hidden;
}

.course-meta {
    font-size: 0.875rem;
    color: var(--text-light);
}

/* Course Detail */
.course-detail {
    display: grid;
    grid-template-columns: 2fr 1fr;
    gap: 2rem;
}

.course-video-section {
    grid-column: 1 / -1;
}

.video-wrapper {
    position: relative;
    width: 100%;
    padding-top: 56.25%; /* 16:9 */
    margin-bottom: 2rem;
    background-color: #000;
    border-radius: 0.75rem;
    overflow: hidden;
}

.video-wrapper iframe {
    position: absolute;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
}

.course-detail-info {
    background-color: var(--bg-color);
    padding: 1.5rem;
    border-radius: 0.75rem;
    box-shadow: var(--shadow);
}

.course-detail-title {
    font-size: 1.75rem;
    margin-bottom: 1rem;
    color: var(--text-color);
}

.course-detail-meta {
    display: flex;
    flex-wrap: wrap;
    gap: 1rem;
    margin-bottom: 1.5rem;
    font-size: 0.875rem;
    color: var(--text-light);
}

.badge {
    padding: 0.25rem 0.75rem;
    background-color: var(--primary-color);
    color: white;
    border-radius: 1rem;
    font-size: 0.875rem;
    font-weight: 500;
}

.course-detail-description h3 {
    font-size: 1.25rem;
    margin-bottom: 0.5rem;
    color: var(--text-color);
}

.course-detail-description p {
    color: var(--text-light);
    line-height: 1.8;
}

.related-courses {
    margin-top: 3rem;
}

.related-courses h2 {
    font-size: 1.5rem;
    margin-bottom: 1.5rem;
    color: var(--text-color);
}

/* No Courses */
.no-courses {
    text-align: center;
    padding: 3rem;
    background-color: var(--bg-color);
    border-radius: 0.75rem;
    box-shadow: var(--shadow);
}

.no-courses p {
    font-size: 1.125rem;
    color: var(--text-light);
    margin-bottom: 1rem;
}

/* Buttons */
.btn-primary {
    display: inline-block;
    padding: 0.75rem 1.5rem;
    background-color: var(--primary-color);
    color: white;
    text-decoration: none;
    border-radius: 0.5rem;
    font-weight: 500;
    border: none;
    cursor: pointer;
    transition: background-color 0.2s;
}

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

.btn-secondary {
    display: inline-block;
    padding: 0.75rem 1.5rem;
    background-color: var(--bg-color);
    color: var(--text-color);
    text-decoration: none;
    border-radius: 0.5rem;
    font-weight: 500;
    border: 1px solid var(--border-color);
    transition: border-color 0.2s;
}

.btn-secondary:hover {
    border-color: var(--primary-color);
}

/* Admin Page */
.page-title {
    font-size: 2rem;
    margin-bottom: 2rem;
    color: var(--text-color);
}

.admin-section {
    background-color: var(--bg-color);
    padding: 2rem;
    border-radius: 0.75rem;
    box-shadow: var(--shadow);
    margin-bottom: 2rem;
}

.admin-section h2 {
    font-size: 1.5rem;
    margin-bottom: 1.5rem;
    color: var(--text-color);
}

.course-form {
    max-width: 600px;
}

.form-group {
    margin-bottom: 1.5rem;
}

.form-group label {
    display: block;
    margin-bottom: 0.5rem;
    font-weight: 500;
    color: var(--text-color);
}

.form-group input,
.form-group textarea {
    width: 100%;
    padding: 0.75rem;
    border: 1px solid var(--border-color);
    border-radius: 0.5rem;
    font-size: 1rem;
    font-family: inherit;
    transition: border-color 0.2s;
}

.form-group input:focus,
.form-group textarea:focus {
    outline: none;
    border-color: var(--primary-color);
}

.form-group small {
    display: block;
    margin-top: 0.25rem;
    font-size: 0.875rem;
    color: var(--text-light);
}

.form-actions {
    display: flex;
    gap: 1rem;
}

.message {
    padding: 1rem;
    border-radius: 0.5rem;
    margin-bottom: 1.5rem;
}

.message.success {
    background-color: #d1fae5;
    color: #065f46;
    border: 1px solid #6ee7b7;
}

.message.error {
    background-color: #fee2e2;
    color: #991b1b;
    border: 1px solid #fca5a5;
}

.courses-table {
    width: 100%;
    border-collapse: collapse;
}

.courses-table th,
.courses-table td {
    padding: 0.75rem;
    text-align: left;
    border-bottom: 1px solid var(--border-color);
}

.courses-table th {
    background-color: var(--bg-light);
    font-weight: 600;
    color: var(--text-color);
}

.courses-table td a {
    color: var(--primary-color);
    text-decoration: none;
}

.courses-table td a:hover {
    text-decoration: underline;
}

.actions {
    display: flex;
    gap: 0.5rem;
}

.btn-edit {
    padding: 0.5rem 1rem;
    background-color: var(--primary-color);
    color: white;
    text-decoration: none;
    border-radius: 0.375rem;
    font-size: 0.875rem;
    transition: background-color 0.2s;
}

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

.btn-delete {
    padding: 0.5rem 1rem;
    background-color: #ef4444;
    color: white;
    border: none;
    border-radius: 0.375rem;
    font-size: 0.875rem;
    cursor: pointer;
    transition: background-color 0.2s;
}

.btn-delete:hover {
    background-color: #dc2626;
}

/* Footer */
.footer {
    background-color: var(--bg-color);
    border-top: 1px solid var(--border-color);
    padding: 2rem 0;
    margin-top: 3rem;
    text-align: left;
    color: var(--text-light);
}

/* Course Tabs */
.course-tabs {
    display: flex;
    gap: 0;
    margin-bottom: 2rem;
}

.course-tab {
    padding: 1rem 1.5rem;
    text-decoration: none;
    color: var(--text-light);
    border-bottom: 2px solid transparent;
    transition: all 0.2s;
    font-weight: 500;
}

.course-tab:hover {
    color: var(--primary-color);
    border-bottom-color: var(--primary-color);
}

.course-tab.active {
    color: var(--primary-color);
    border-bottom-color: var(--primary-color);
}

/* Playlist Container */
.playlist-container {
    display: flex;
    min-height: calc(100vh - 200px);
}

@media (max-width: 1024px) {
    .playlist-container {
        flex-direction: column;
    }
    
    .playlist-sidebar {
        width: 100% !important;
        max-height: 400px !important;
    }
}

/* Question Styles */
.question-card {
    background: white;
    border-radius: 0.75rem;
    box-shadow: var(--shadow);
    padding: 1.5rem;
    margin-bottom: 1.5rem;
    cursor: pointer;
    transition: transform 0.2s, box-shadow 0.2s;
}

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

.question-card-header {
    display: flex;
    justify-content: space-between;
    align-items: start;
    margin-bottom: 1rem;
    gap: 1rem;
}

.question-card-title {
    font-size: 1.25rem;
    margin: 0;
    color: var(--text-color);
    flex: 1;
}

.question-card-title a {
    text-decoration: none;
    color: inherit;
}

.question-card-images {
    display: flex;
    gap: 0.5rem;
    margin-bottom: 1rem;
    flex-wrap: wrap;
}

.question-card-image {
    width: 150px;
    height: 150px;
    object-fit: cover;
    border-radius: 0.5rem;
    box-shadow: 0 2px 8px rgba(0,0,0,0.1);
}

.question-card-content {
    color: var(--text-color);
    line-height: 1.8;
    margin-bottom: 1rem;
    display: -webkit-box;
    -webkit-line-clamp: 3;
    -webkit-box-orient: vertical;
    overflow: hidden;
    text-overflow: ellipsis;
}

.question-card-meta {
    font-size: 0.875rem;
    color: var(--text-light);
}

.question-list-header {
    display: flex;
    justify-content: space-between;
    align-items: center;
    margin-bottom: 2rem;
    flex-wrap: wrap;
    gap: 1rem;
}

.question-detail-container {
    max-width: 800px;
    margin: 0 auto;
}

.question-header {
    margin-bottom: 2rem;
}

.question-title {
    font-size: 2rem;
    margin-bottom: 1rem;
    color: var(--text-color);
    word-break: break-word;
}

.question-meta {
    font-size: 0.875rem;
    color: var(--text-light);
    margin-bottom: 2rem;
}

.question-content {
    background: white;
    border-radius: 0.75rem;
    box-shadow: var(--shadow);
    padding: 2rem;
    margin-bottom: 2rem;
}

.question-content-text {
    color: var(--text-color);
    line-height: 1.8;
    white-space: pre-wrap;
    font-size: 1.125rem;
    word-break: break-word;
}

.question-images {
    display: grid;
    grid-template-columns: repeat(auto-fill, minmax(300px, 1fr));
    gap: 1rem;
    margin-top: 2rem;
}

.question-image {
    width: 100%;
    max-width: 600px;
    max-height: 500px;
    height: auto;
    border-radius: 0.5rem;
    box-shadow: 0 2px 8px rgba(0,0,0,0.1);
    object-fit: contain;
    background: #f9fafb;
}

.question-actions {
    display: flex;
    gap: 1rem;
    margin-top: 2rem;
    flex-wrap: wrap;
}

/* Mobile Menu */
.mobile-menu-toggle {
    display: none;
    background: none;
    border: none;
    font-size: 1.5rem;
    cursor: pointer;
    color: var(--text-color);
    padding: 0.5rem;
}

.mobile-nav {
    display: none;
    flex-direction: column;
    gap: 0.5rem;
    margin-top: 1rem;
    padding-top: 1rem;
    border-top: 1px solid var(--border-color);
}

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

/* Responsive */
@media (max-width: 1024px) {
    .question-images {
        grid-template-columns: repeat(auto-fill, minmax(250px, 1fr));
    }
    
    .question-image {
        max-width: 100%;
    }
    
    .admin-section {
        padding: 1.5rem;
    }
    
    .courses-table {
        font-size: 0.875rem;
    }
}

@media (max-width: 768px) {
    .container {
        padding: 0 15px;
    }
    
    .courses-grid {
        grid-template-columns: 1fr;
    }
    
    .course-detail {
        grid-template-columns: 1fr;
    }
    
    .hero h2 {
        font-size: 2rem;
    }
    
    .hero {
        padding: 2rem 0;
    }
    
    .header-content {
        flex-wrap: wrap;
    }
    
    .nav {
        display: none;
    }
    
    .mobile-menu-toggle {
        display: block;
    }
    
    .mobile-nav {
        display: none;
        width: 100%;
    }
    
    .mobile-nav.active {
        display: flex;
    }
    
    .mobile-nav a {
        padding: 0.75rem;
        border-radius: 0.5rem;
        transition: background-color 0.2s;
    }
    
    .mobile-nav a:hover {
        background-color: var(--bg-light);
    }
    
    .courses-table {
        font-size: 0.75rem;
        display: block;
        overflow-x: auto;
        -webkit-overflow-scrolling: touch;
    }
    
    .courses-table th,
    .courses-table td {
        padding: 0.5rem 0.25rem;
        white-space: nowrap;
    }
    
    .course-tabs {
        flex-wrap: wrap;
    }
    
    .course-tab {
        padding: 0.75rem 1rem;
        font-size: 0.875rem;
    }
    
    .learn-points-grid {
        grid-template-columns: 1fr !important;
    }
    
    .page-title {
        font-size: 1.5rem;
    }
    
    .question-list-header {
        flex-direction: column;
        align-items: stretch;
    }
    
    .question-list-header .btn-primary {
        width: 100%;
        text-align: center;
    }
    
    .question-card {
        padding: 1rem;
    }
    
    .question-card-header {
        flex-direction: column;
        align-items: stretch;
    }
    
    .question-card-title {
        font-size: 1.125rem;
        margin-bottom: 0.5rem;
    }
    
    .question-card-images {
        gap: 0.5rem;
    }
    
    .question-card-image {
        width: 100px;
        height: 100px;
    }
    
    .question-title {
        font-size: 1.5rem;
    }
    
    .question-content {
        padding: 1.5rem;
    }
    
    .question-content-text {
        font-size: 1rem;
    }
    
    .question-images {
        grid-template-columns: 1fr;
        gap: 1rem;
    }
    
    .question-image {
        max-width: 100%;
        max-height: 400px;
    }
    
    .images-preview img {
        max-width: 100% !important;
        width: 100% !important;
    }
    
    #image_urls_container {
        display: flex;
        flex-direction: column;
        gap: 0.5rem;
    }
    
    #image_urls_container > div {
        display: flex;
        flex-direction: column;
        gap: 0.5rem;
    }
    
    #image_urls_container input {
        width: 100% !important;
    }
    
    #image_urls_container button {
        width: 100%;
    }
    
    .question-actions {
        flex-direction: column;
    }
    
    .question-actions .btn-edit,
    .question-actions .btn-secondary {
        width: 100%;
        text-align: center;
    }
    
    .admin-section {
        padding: 1rem;
    }
    
    .admin-section h2 {
        font-size: 1.25rem;
    }
    
    .course-form {
        max-width: 100%;
    }
    
    .form-group {
        margin-bottom: 1rem;
    }
    
    .form-group input,
    .form-group textarea {
        font-size: 16px; /* iOS 줌 방지 */
    }
    
    .form-actions {
        flex-direction: column;
    }
    
    .form-actions .btn-primary,
    .form-actions .btn-secondary {
        width: 100%;
        text-align: center;
    }
    
    .btn-primary,
    .btn-secondary,
    .btn-edit,
    .btn-delete {
        padding: 0.875rem 1.25rem;
        font-size: 1rem;
        min-height: 44px; /* 터치 영역 최소 크기 */
    }
    
    .main {
        padding: 1.5rem 0;
    }
    
    .footer {
        padding: 1.5rem 0;
    }
}

@media (max-width: 480px) {
    .container {
        padding: 0 10px;
    }
    
    h1.logo,
    .logo {
        font-size: 0;
        height: 1.98rem;
        line-height: 1.98rem;
        font-weight: normal;
    }
    
    h1.logo img,
    h1.logo a img,
    .logo img,
    .logo a img {
        max-height: 1.98rem !important;
        height: 1.98rem !important;
        max-width: 238px !important;
    }
    
    h1.logo a,
    .logo a {
        height: 1.98rem;
    }
    
    .hero h2 {
        font-size: 1.75rem;
    }
    
    .hero p {
        font-size: 1rem;
    }
    
    .page-title {
        font-size: 1.25rem;
    }
    
    .question-card {
        padding: 0.75rem;
    }
    
    .question-card-image {
        width: 80px;
        height: 80px;
    }
    
    .question-title {
        font-size: 1.25rem;
    }
    
    .question-content {
        padding: 1rem;
    }
    
    .question-content-text {
        font-size: 0.9375rem;
    }
    
    .admin-section {
        padding: 0.75rem;
    }
    
    .admin-tabs {
        flex-wrap: wrap;
    }
    
    .admin-tab {
        padding: 0.75rem 1rem;
        font-size: 0.875rem;
    }
    
    .form-group label input[type="checkbox"] {
        width: auto;
        margin-right: 0.5rem;
    }
    
    .form-group > div[style*="display: flex"] {
        flex-direction: column;
    }
    
    .form-group > div[style*="display: flex"] > div {
        width: 100%;
    }
    
    .form-group > div[style*="display: flex"] img {
        max-width: 100% !important;
        width: 100% !important;
        height: auto !important;
    }
}