:root {
    --color-primary: #2563eb;
    --color-primary-light: #dbeafe;
    --color-primary-dark: #1d4ed8;
    --color-secondary: #0891b2;
    --color-accent: #f59e0b;
    --color-success: #10b981;
    --color-danger: #ef4444;
    --color-text: #1e293b;
    --color-text-light: #64748b;
    --color-bg: #f8fafc;
    --color-white: #ffffff;
    --color-border: #e2e8f0;
    
    --radius-sm: 8px;
    --radius-md: 12px;
    --radius-lg: 16px;
    
    --shadow-sm: 0 1px 2px rgba(0,0,0,0.05);
    --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);
    
    --transition: all 0.3s cubic-bezier(0.4, 0, 0.2, 1);
}

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

body {
    font-family: 'Noto Sans SC', -apple-system, BlinkMacSystemFont, sans-serif;
    background-color: var(--color-bg);
    color: var(--color-text);
    line-height: 1.6;
    -webkit-font-smoothing: antialiased;
    min-height: 100vh;
}

.page {
    display: none;
    min-height: 100vh;
}

.page.active {
    display: flex;
    flex-direction: column;
}

/* Header */
.app-header {
    background: var(--color-white);
    padding: 16px 20px;
    display: flex;
    justify-content: space-between;
    align-items: center;
    box-shadow: var(--shadow-sm);
    position: sticky;
    top: 0;
    z-index: 100;
}

.header-left {
    display: flex;
    align-items: center;
    gap: 12px;
}

.header-logo {
    width: 40px;
    height: 40px;
    border-radius: var(--radius-sm);
    object-fit: cover;
}

.user-name {
    font-size: 18px;
    font-weight: 600;
    color: var(--color-text);
    margin: 0;
}

.user-role {
    font-size: 13px;
    color: var(--color-text-light);
    margin: 0;
}

.icon-btn {
    width: 44px;
    height: 44px;
    border: none;
    background: transparent;
    border-radius: 50%;
    cursor: pointer;
    display: flex;
    align-items: center;
    justify-content: center;
    transition: var(--transition);
    position: relative;
}

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

.icon-btn .badge {
    position: absolute;
    top: 6px;
    right: 6px;
    background: var(--color-danger);
    color: white;
    font-size: 11px;
    padding: 2px 6px;
    border-radius: 10px;
    min-width: 18px;
    text-align: center;
}

.page-title {
    font-size: 18px;
    font-weight: 600;
    color: var(--color-text);
}

/* Main Content */
.main-content {
    flex: 1;
    padding: 20px;
    padding-bottom: 100px;
    overflow-y: auto;
}

.section-title {
    font-size: 16px;
    font-weight: 600;
    color: var(--color-text);
    margin-bottom: 16px;
}

.section-header {
    display: flex;
    justify-content: space-between;
    align-items: center;
    margin-bottom: 12px;
}

.see-all {
    font-size: 14px;
    color: var(--color-primary);
    background: none;
    border: none;
    cursor: pointer;
}

/* Quick Actions */
.quick-actions {
    margin-bottom: 32px;
}

.action-grid {
    display: grid;
    grid-template-columns: repeat(4, 1fr);
    gap: 12px;
}

.action-card {
    background: var(--color-white);
    border: none;
    border-radius: var(--radius-md);
    padding: 16px 8px;
    cursor: pointer;
    transition: var(--transition);
    box-shadow: var(--shadow-sm);
    display: flex;
    flex-direction: column;
    align-items: center;
    gap: 8px;
}

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

.action-icon {
    width: 56px;
    height: 56px;
    border-radius: var(--radius-md);
    display: flex;
    align-items: center;
    justify-content: center;
    background: var(--color-primary-light);
}

.grade-icon { background: #dbeafe; }
.class-icon { background: #cffafe; }
.wrong-icon { background: #fef3c7; }
.overview-icon { background: #d1fae5; }

.action-name {
    font-size: 13px;
    color: var(--color-text);
    margin: 0;
    font-weight: 500;
}

/* Class Cards */
.class-list {
    display: flex;
    flex-direction: column;
    gap: 12px;
}

.class-card {
    background: var(--color-white);
    border-radius: var(--radius-md);
    padding: 16px;
    box-shadow: var(--shadow-sm);
    display: flex;
    justify-content: space-between;
    align-items: center;
    cursor: pointer;
    transition: var(--transition);
}

.class-card:hover {
    box-shadow: var(--shadow-md);
}

.class-name {
    font-size: 16px;
    font-weight: 600;
    color: var(--color-text);
    margin-bottom: 8px;
}

.class-meta {
    display: flex;
    gap: 16px;
}

.meta-item {
    display: flex;
    align-items: center;
    gap: 4px;
    font-size: 13px;
    color: var(--color-text-light);
}

.class-stat {
    text-align: right;
}

.stat-value {
    font-size: 24px;
    font-weight: 700;
    color: var(--color-primary);
}

.stat-label {
    font-size: 12px;
    color: var(--color-text-light);
}

/* Bottom Navigation */
.bottom-nav {
    position: fixed;
    bottom: 0;
    left: 0;
    right: 0;
    background: var(--color-white);
    box-shadow: 0 -2px 10px rgba(0,0,0,0.05);
    display: flex;
    justify-content: space-around;
    padding: 8px 0;
    z-index: 100;
}

.nav-item {
    flex: 1;
    display: flex;
    flex-direction: column;
    align-items: center;
    gap: 4px;
    background: none;
    border: none;
    padding: 8px;
    cursor: pointer;
    color: var(--color-text-light);
    transition: var(--transition);
}

.nav-item.active {
    color: var(--color-primary);
}

.nav-item span {
    font-size: 11px;
}

/* Login Page */
.login-container {
    min-height: 100vh;
    padding: 60px 24px 40px;
    display: flex;
    flex-direction: column;
    background: linear-gradient(180deg, #eff6ff 0%, #f8fafc 100%);
}

.logo-section {
    text-align: center;
    margin-bottom: 48px;
}

.logo {
    width: 80px;
    height: 80px;
    border-radius: var(--radius-lg);
    object-fit: cover;
    margin-bottom: 16px;
}

.app-name {
    font-family: 'Poppins', 'Noto Sans SC', sans-serif;
    font-size: 32px;
    font-weight: 700;
    color: var(--color-primary);
    margin: 0 0 4px;
}

.app-tagline {
    font-size: 14px;
    color: var(--color-text-light);
    margin: 0;
}

.form-section {
    background: var(--color-white);
    border-radius: var(--radius-lg);
    padding: 32px 24px;
    box-shadow: var(--shadow-md);
}

.form-tabs {
    display: flex;
    gap: 8px;
    margin-bottom: 24px;
    background: var(--color-bg);
    border-radius: var(--radius-md);
    padding: 4px;
}

.tab-btn {
    flex: 1;
    padding: 10px 16px;
    border: none;
    background: transparent;
    border-radius: var(--radius-sm);
    cursor: pointer;
    font-size: 15px;
    font-weight: 500;
    color: var(--color-text-light);
    transition: var(--transition);
}

.tab-btn.active {
    background: var(--color-white);
    color: var(--color-primary);
    box-shadow: var(--shadow-sm);
}

.form {
    display: none;
}

.form.active {
    display: flex;
    flex-direction: column;
    gap: 20px;
}

.input-group {
    display: flex;
    flex-direction: column;
    gap: 8px;
}

.input-group label {
    font-size: 14px;
    font-weight: 500;
    color: var(--color-text);
}

.input-group input {
    padding: 14px 16px;
    border: 1px solid var(--color-border);
    border-radius: var(--radius-md);
    font-size: 15px;
    transition: var(--transition);
}

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

.primary-btn {
    background: var(--color-primary);
    color: white;
    border: none;
    padding: 14px 24px;
    border-radius: var(--radius-md);
    font-size: 16px;
    font-weight: 600;
    cursor: pointer;
    transition: var(--transition);
}

.primary-btn:hover {
    background: var(--color-primary-dark);
    transform: translateY(-1px);
}

.secondary-btn {
    background: var(--color-white);
    color: var(--color-text);
    border: 1px solid var(--color-border);
    padding: 14px 24px;
    border-radius: var(--radius-md);
    font-size: 16px;
    font-weight: 500;
    cursor: pointer;
    transition: var(--transition);
}

.forgot-password {
    text-align: center;
    font-size: 14px;
    color: var(--color-primary);
    margin: 8px 0 0;
    cursor: pointer;
}

/* Upload Area */
.upload-area {
    background: var(--color-white);
    border-radius: var(--radius-lg);
    padding: 48px 24px;
    text-align: center;
    box-shadow: var(--shadow-sm);
    border: 2px dashed var(--color-border);
}

.upload-content {
    position: relative;
}

.upload-icon {
    margin-bottom: 20px;
}

.upload-text {
    font-size: 16px;
    font-weight: 500;
    color: var(--color-text);
    margin: 0 0 8px;
}

.upload-hint {
    font-size: 13px;
    color: var(--color-text-light);
    margin: 0;
}

#file-input {
    position: absolute;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    opacity: 0;
    cursor: pointer;
}

.preview-area {
    background: var(--color-white);
    border-radius: var(--radius-lg);
    padding: 20px;
    box-shadow: var(--shadow-sm);
}

#preview-image {
    width: 100%;
    border-radius: var(--radius-md);
    margin-bottom: 16px;
}

.preview-controls {
    display: flex;
    gap: 12px;
}

.preview-controls button {
    flex: 1;
}

/* Grading Progress */
.grading-progress {
    background: var(--color-white);
    border-radius: var(--radius-lg);
    padding: 48px 24px;
    text-align: center;
    box-shadow: var(--shadow-sm);
}

.loading-spinner {
    position: relative;
    width: 80px;
    height: 80px;
    margin: 0 auto 24px;
}

.spinner-ring {
    position: absolute;
    width: 64px;
    height: 64px;
    border: 4px solid transparent;
    border-top-color: var(--color-primary);
    border-radius: 50%;
    animation: spin 1.2s linear infinite;
}

.spinner-ring:nth-child(1) { top: 8px; left: 8px; animation-delay: -0.45s; }
.spinner-ring:nth-child(2) { top: 8px; left: 8px; animation-delay: -0.3s; border-top-color: var(--color-secondary); }
.spinner-ring:nth-child(3) { top: 8px; left: 8px; animation-delay: -0.15s; border-top-color: var(--color-accent); }

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

.progress-text {
    font-size: 18px;
    font-weight: 600;
    color: var(--color-text);
    margin: 0 0 8px;
}

.progress-hint {
    font-size: 14px;
    color: var(--color-text-light);
    margin: 0;
}

/* Overview Cards */
.overview-cards {
    display: grid;
    grid-template-columns: 1fr 1fr;
    gap: 16px;
    margin-bottom: 32px;
}

.overview-card {
    background: var(--color-white);
    border-radius: var(--radius-lg);
    padding: 20px 16px;
    box-shadow: var(--shadow-sm);
}

.overview-card.primary {
    background: linear-gradient(135deg, #2563eb 0%, #1d4ed8 100%);
    color: white;
}

.overview-card.secondary {
    background: linear-gradient(135deg, #0891b2 0%, #0e7490 100%);
    color: white;
}

.overview-label {
    font-size: 13px;
    opacity: 0.9;
    margin-bottom: 8px;
}

.overview-value {
    font-size: 32px;
    font-weight: 700;
    margin-bottom: 8px;
}

.overview-change {
    display: inline-flex;
    align-items: center;
    gap: 4px;
    font-size: 13px;
    opacity: 0.95;
}

.overview-change.up {
    color: #bbf7d0;
}

/* Weak Points */
.weak-list {
    display: flex;
    flex-direction: column;
    gap: 12px;
}

.weak-item {
    background: var(--color-white);
    border-radius: var(--radius-md);
    padding: 16px;
    box-shadow: var(--shadow-sm);
    display: flex;
    align-items: center;
    gap: 16px;
}

.weak-rank {
    width: 32px;
    height: 32px;
    border-radius: 50%;
    background: var(--color-primary-light);
    color: var(--color-primary);
    display: flex;
    align-items: center;
    justify-content: center;
    font-weight: 700;
    font-size: 14px;
    flex-shrink: 0;
}

.weak-content {
    flex: 1;
}

.weak-name {
    font-size: 15px;
    font-weight: 600;
    margin-bottom: 4px;
}

.weak-meta {
    font-size: 13px;
    color: var(--color-text-light);
}

.weak-bar {
    width: 60px;
    height: 6px;
    background: var(--color-border);
    border-radius: 3px;
    overflow: hidden;
}

.weak-progress {
    height: 100%;
    background: linear-gradient(90deg, var(--color-danger), var(--color-accent));
    border-radius: 3px;
    transition: width 1s ease;
}