/* CSS 변수 정의 */
:root {
    --primary-color: #4285f4;
    --primary-hover: #357ae8;
    --secondary-color: #34a853;
    --danger-color: #ea4335;
    --warning-color: #fbbc04;
    --bg-primary: #ffffff;
    --bg-secondary: #f5f5f5;
    --bg-tertiary: #e8e8e8;
    --text-primary: #202124;
    --text-secondary: #5f6368;
    --text-tertiary: #80868b;
    --border-color: #dadce0;
    --shadow-sm: 0 1px 2px 0 rgba(60,64,67,0.1), 0 1px 3px 1px rgba(60,64,67,0.08);
    --shadow-md: 0 1px 3px 0 rgba(60,64,67,0.12), 0 4px 8px 3px rgba(60,64,67,0.08);
    --shadow-lg: 0 1px 8px 0 rgba(60,64,67,0.12), 0 8px 16px 8px rgba(60,64,67,0.08);
    --radius-sm: 4px;
    --radius-md: 8px;
    --radius-lg: 16px;
    --transition: all 0.3s cubic-bezier(0.4, 0, 0.2, 1);
}

/* 다크 모드 */
@media (prefers-color-scheme: dark) {
    :root {
        --bg-primary: #1a1a1a;
        --bg-secondary: #2d2d2d;
        --bg-tertiary: #404040;
        --text-primary: #e8eaed;
        --text-secondary: #9aa0a6;
        --text-tertiary: #80868b;
        --border-color: #5f6368;
    }
}

/* 기본 스타일 초기화 */
* {
    margin: 0;
    padding: 0;
    box-sizing: border-box;
}

html, body {
    height: 100%;
    font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, 'Helvetica Neue', Arial, sans-serif;
    font-size: 16px;
    color: var(--text-primary);
    background-color: var(--bg-primary);
    line-height: 1.5;
    -webkit-font-smoothing: antialiased;
    -moz-osx-font-smoothing: grayscale;
}

/* 앱 컨테이너 */
#app {
    display: flex;
    flex-direction: column;
    min-height: 100vh;
}

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

.header-content {
    max-width: 1400px;
    margin: 0 auto;
    padding: 1rem 1.5rem;
    display: flex;
    justify-content: space-between;
    align-items: center;
}

.app-title {
    font-size: 1.5rem;
    font-weight: 600;
    color: var(--text-primary);
}

.header-actions {
    display: flex;
    align-items: center;
    gap: 1rem;
}

.user-info {
    display: flex;
    align-items: center;
    gap: 0.75rem;
}

#userEmail {
    color: var(--text-secondary);
    font-size: 0.875rem;
}

/* 메인 컨텐츠 */
.main-content {
    flex: 1;
    max-width: 1400px;
    width: 100%;
    margin: 0 auto;
    padding: 2rem 1.5rem;
}

/* 버튼 스타일 */
.btn-primary, .btn-secondary, .btn-icon {
    border: none;
    cursor: pointer;
    font-size: 0.875rem;
    font-weight: 500;
    transition: var(--transition);
    outline: none;
    display: inline-flex;
    align-items: center;
    justify-content: center;
    gap: 0.5rem;
}

.btn-primary {
    background-color: var(--primary-color);
    color: white;
    padding: 0.75rem 1.5rem;
    border-radius: var(--radius-md);
}

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

.btn-secondary {
    background-color: transparent;
    color: var(--primary-color);
    padding: 0.5rem 1rem;
    border: 1px solid var(--border-color);
    border-radius: var(--radius-md);
}

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

.btn-icon {
    background-color: transparent;
    color: var(--text-secondary);
    padding: 0.5rem;
    border-radius: 50%;
    width: 40px;
    height: 40px;
}

.btn-icon:hover {
    background-color: var(--bg-secondary);
    color: var(--text-primary);
}

/* 인증 섹션 */
.auth-section {
    display: flex;
    justify-content: center;
    align-items: center;
    min-height: 60vh;
}

.auth-card {
    background-color: var(--bg-primary);
    border-radius: var(--radius-lg);
    box-shadow: var(--shadow-lg);
    padding: 3rem;
    max-width: 400px;
    width: 100%;
    text-align: center;
}

.auth-card h2 {
    margin-bottom: 1rem;
    font-size: 1.75rem;
    color: var(--text-primary);
}

.auth-card p {
    color: var(--text-secondary);
    margin-bottom: 2rem;
}

.auth-info {
    margin-top: 2rem;
    text-align: left;
}

.auth-info h3 {
    font-size: 1rem;
    color: var(--text-primary);
    margin-bottom: 0.5rem;
}

.auth-info ul {
    list-style: none;
    padding-left: 0;
    color: var(--text-secondary);
    font-size: 0.875rem;
}

.auth-info ul li {
    padding: 0.25rem 0;
    padding-left: 1.5rem;
    position: relative;
}

.auth-info ul li::before {
    content: '✓';
    position: absolute;
    left: 0;
    color: var(--secondary-color);
}

.privacy-note {
    margin-top: 1rem;
    padding-top: 1rem;
    border-top: 1px solid var(--border-color);
    font-size: 0.75rem;
    color: var(--text-tertiary);
}

/* 책 섹션 */
.books-section {
    width: 100%;
}

/* 로딩 상태 */
.loading-state {
    display: flex;
    flex-direction: column;
    align-items: center;
    justify-content: center;
    min-height: 40vh;
    gap: 1rem;
}

.spinner {
    width: 48px;
    height: 48px;
    border: 4px solid var(--bg-tertiary);
    border-top-color: var(--primary-color);
    border-radius: 50%;
    animation: spin 1s linear infinite;
}

@keyframes spin {
    to { transform: rotate(360deg); }
}

/* 책 그리드 */
.books-grid {
    display: grid;
    grid-template-columns: repeat(auto-fill, minmax(200px, 1fr));
    gap: 1.5rem;
    animation: fadeIn 0.3s ease-in;
}

@keyframes fadeIn {
    from { opacity: 0; transform: translateY(10px); }
    to { opacity: 1; transform: translateY(0); }
}

/* 책 카드 */
.book-card {
    background-color: var(--bg-primary);
    border-radius: var(--radius-md);
    overflow: hidden;
    box-shadow: var(--shadow-sm);
    transition: var(--transition);
    cursor: pointer;
    display: flex;
    flex-direction: column;
}

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

.book-cover {
    position: relative;
    padding-top: 140%; /* 책 표지 비율 (세로가 더 긴 직사각형) */
    background-color: var(--bg-secondary);
    overflow: hidden;
}

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

.book-cover-placeholder {
    position: absolute;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    display: flex;
    align-items: center;
    justify-content: center;
    background: linear-gradient(135deg, var(--bg-secondary), var(--bg-tertiary));
}

.book-cover-placeholder svg {
    width: 48px;
    height: 48px;
    color: var(--text-tertiary);
}

.book-info {
    padding: 1rem;
    flex: 1;
    display: flex;
    flex-direction: column;
}

.book-title {
    font-size: 0.875rem;
    font-weight: 600;
    color: var(--text-primary);
    margin-bottom: 0.5rem;
    overflow: hidden;
    text-overflow: ellipsis;
    display: -webkit-box;
    -webkit-line-clamp: 2;
    -webkit-box-orient: vertical;
}

.book-meta {
    display: flex;
    flex-direction: column;
    gap: 0.25rem;
    font-size: 0.75rem;
    color: var(--text-secondary);
}

.book-pages {
    display: flex;
    align-items: center;
    gap: 0.25rem;
}

.book-date {
    display: flex;
    align-items: center;
    gap: 0.25rem;
}

.book-progress {
    margin-top: 0.5rem;
    background-color: var(--bg-secondary);
    height: 4px;
    border-radius: 2px;
    overflow: hidden;
}

.book-progress-bar {
    height: 100%;
    background-color: var(--primary-color);
    transition: width 0.3s ease;
}

/* 빈 상태 */
.empty-state, .error-state {
    display: flex;
    flex-direction: column;
    align-items: center;
    justify-content: center;
    min-height: 40vh;
    text-align: center;
    gap: 1rem;
}

.empty-state svg, .error-state svg {
    color: var(--text-tertiary);
}

.empty-state h3, .error-state h3 {
    font-size: 1.25rem;
    color: var(--text-primary);
}

.empty-state p, .error-state p {
    color: var(--text-secondary);
    margin-bottom: 1rem;
}

.error-state svg {
    color: var(--danger-color);
}

/* 반응형 디자인 */
@media (max-width: 768px) {
    .header-content {
        padding: 0.75rem 1rem;
    }
    
    .app-title {
        font-size: 1.25rem;
    }
    
    .main-content {
        padding: 1rem;
    }
    
    .auth-card {
        padding: 2rem 1.5rem;
    }
    
    .books-grid {
        grid-template-columns: repeat(auto-fill, minmax(150px, 1fr));
        gap: 1rem;
    }
}

@media (max-width: 480px) {
    .books-grid {
        grid-template-columns: repeat(auto-fill, minmax(120px, 1fr));
    }
    
    #userEmail {
        display: none;
    }
}

/* 접근성 */
:focus-visible {
    outline: 2px solid var(--primary-color);
    outline-offset: 2px;
}

/* 스크롤바 스타일 */
::-webkit-scrollbar {
    width: 8px;
    height: 8px;
}

::-webkit-scrollbar-track {
    background: var(--bg-secondary);
}

::-webkit-scrollbar-thumb {
    background: var(--text-tertiary);
    border-radius: 4px;
}

::-webkit-scrollbar-thumb:hover {
    background: var(--text-secondary);
}