/* ========================================
   Learn Platform — Black & White Minimal UI
   ======================================== */

:root {
    --bg: #000000;
    --card: #111111;
    --secondary: #181818;
    --text: #FFFFFF;
    --text-secondary: #A0A0A0;
    --border: #2A2A2A;
    --hover: #1a1a1a;
    --radius: 8px;
    --radius-sm: 6px;
    --font: system-ui, -apple-system, 'Segoe UI', Roboto, 'Helvetica Neue', Arial, sans-serif;
}

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

html {
    font-size: 16px;
    -webkit-text-size-adjust: 100%;
}

body {
    font-family: var(--font);
    background: var(--bg);
    color: var(--text);
    line-height: 1.5;
    min-height: 100vh;
}

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

a:hover {
    text-decoration: underline;
}

/* ========== Layout ========== */

.app-layout {
    display: flex;
    min-height: 100vh;
}

.sidebar {
    width: 240px;
    background: var(--card);
    border-right: 1px solid var(--border);
    display: flex;
    flex-direction: column;
    position: fixed;
    top: 0;
    left: 0;
    bottom: 0;
    z-index: 100;
    transition: transform 0.2s ease;
}

.sidebar-header {
    padding: 1.25rem 1.5rem;
    border-bottom: 1px solid var(--border);
}

.logo {
    font-size: 1.25rem;
    font-weight: 600;
    letter-spacing: -0.02em;
    text-decoration: none;
}

.logo:hover {
    text-decoration: none;
}

.sidebar-nav {
    flex: 1;
    padding: 1rem 0.75rem;
    display: flex;
    flex-direction: column;
    gap: 0.25rem;
}

.nav-item {
    display: block;
    padding: 0.625rem 0.875rem;
    border-radius: var(--radius-sm);
    color: var(--text-secondary);
    font-size: 0.9375rem;
    transition: background 0.15s, color 0.15s;
    text-decoration: none;
}

.nav-item:hover {
    background: var(--hover);
    color: var(--text);
    text-decoration: none;
}

.nav-item.active {
    background: var(--secondary);
    color: var(--text);
    font-weight: 500;
}

.sidebar-footer {
    padding: 1rem 1.25rem;
    border-top: 1px solid var(--border);
    display: flex;
    flex-direction: column;
    gap: 0.75rem;
}

.user-info {
    display: flex;
    flex-direction: column;
}

.user-name {
    font-size: 0.875rem;
    font-weight: 500;
}

.user-role {
    font-size: 0.75rem;
    color: var(--text-secondary);
}

.main-content {
    flex: 1;
    margin-left: 240px;
    min-height: 100vh;
    display: flex;
    flex-direction: column;
}

.top-header {
    padding: 1.25rem 2rem;
    border-bottom: 1px solid var(--border);
    background: var(--bg);
    position: sticky;
    top: 0;
    z-index: 50;
}

.page-title {
    font-size: 1.25rem;
    font-weight: 600;
    letter-spacing: -0.01em;
}

.content-area {
    padding: 1.5rem 2rem 3rem;
    flex: 1;
}

/* Mobile menu button */
.mobile-menu-btn {
    display: none;
    position: fixed;
    top: 1rem;
    left: 1rem;
    z-index: 200;
    width: 40px;
    height: 40px;
    background: var(--card);
    border: 1px solid var(--border);
    border-radius: var(--radius-sm);
    cursor: pointer;
    flex-direction: column;
    align-items: center;
    justify-content: center;
    gap: 5px;
    padding: 0;
}

.mobile-menu-btn span {
    display: block;
    width: 18px;
    height: 2px;
    background: var(--text);
}

.sidebar-overlay {
    display: none;
    position: fixed;
    inset: 0;
    background: rgba(0,0,0,0.6);
    z-index: 90;
}

/* ========== Cards ========== */

.card {
    background: var(--card);
    border: 1px solid var(--border);
    border-radius: var(--radius);
    padding: 1.25rem;
}

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

.card-title {
    font-size: 1rem;
    font-weight: 600;
}

.card-grid {
    display: grid;
    grid-template-columns: repeat(auto-fill, minmax(260px, 1fr));
    gap: 1rem;
}

.stats-grid {
    display: grid;
    grid-template-columns: repeat(auto-fill, minmax(180px, 1fr));
    gap: 1rem;
    margin-bottom: 2rem;
}

.stat-card {
    background: var(--card);
    border: 1px solid var(--border);
    border-radius: var(--radius);
    padding: 1.25rem;
}

.stat-value {
    font-size: 1.75rem;
    font-weight: 600;
    letter-spacing: -0.02em;
    margin-bottom: 0.25rem;
}

.stat-label {
    font-size: 0.8125rem;
    color: var(--text-secondary);
}

/* ========== Buttons ========== */

.btn {
    display: inline-flex;
    align-items: center;
    justify-content: center;
    gap: 0.5rem;
    padding: 0.5rem 1rem;
    font-size: 0.875rem;
    font-weight: 500;
    font-family: inherit;
    border-radius: var(--radius-sm);
    border: 1px solid transparent;
    cursor: pointer;
    transition: background 0.15s, border-color 0.15s, color 0.15s;
    text-decoration: none;
    line-height: 1.4;
    white-space: nowrap;
}

.btn:hover {
    text-decoration: none;
}

.btn-primary {
    background: var(--text);
    color: var(--bg);
    border-color: var(--text);
}

.btn-primary:hover {
    background: #e0e0e0;
    border-color: #e0e0e0;
}

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

.btn-secondary:hover {
    background: var(--secondary);
    border-color: #3a3a3a;
}

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

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

.btn-danger {
    background: transparent;
    color: #ccc;
    border-color: var(--border);
}

.btn-danger:hover {
    background: #1a1a1a;
    border-color: #444;
    color: #fff;
}

.btn-sm {
    padding: 0.375rem 0.75rem;
    font-size: 0.8125rem;
}

.btn-block {
    width: 100%;
}

/* ========== Forms ========== */

.form-group {
    margin-bottom: 1.25rem;
}

.form-label {
    display: block;
    font-size: 0.8125rem;
    font-weight: 500;
    color: var(--text-secondary);
    margin-bottom: 0.375rem;
}

.form-control {
    width: 100%;
    padding: 0.625rem 0.875rem;
    font-size: 0.9375rem;
    font-family: inherit;
    color: var(--text);
    background: var(--secondary);
    border: 1px solid var(--border);
    border-radius: var(--radius-sm);
    transition: border-color 0.15s;
    outline: none;
}

.form-control:focus {
    border-color: #555;
}

.form-control::placeholder {
    color: #666;
}

textarea.form-control {
    min-height: 120px;
    resize: vertical;
}

select.form-control {
    appearance: none;
    background-image: url("data:image/svg+xml,%3Csvg xmlns='http://www.w3.org/2000/svg' width='12' height='12' viewBox='0 0 12 12'%3E%3Cpath fill='%23A0A0A0' d='M6 8L1 3h10z'/%3E%3C/svg%3E");
    background-repeat: no-repeat;
    background-position: right 0.75rem center;
    padding-right: 2rem;
}

.form-row {
    display: grid;
    grid-template-columns: 1fr 1fr;
    gap: 1rem;
}

.form-actions {
    display: flex;
    gap: 0.75rem;
    margin-top: 1.5rem;
    flex-wrap: wrap;
}

/* ========== Tables ========== */

.table-wrapper {
    overflow-x: auto;
    border: 1px solid var(--border);
    border-radius: var(--radius);
}

table {
    width: 100%;
    border-collapse: collapse;
    font-size: 0.875rem;
}

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

th {
    background: var(--secondary);
    font-weight: 500;
    color: var(--text-secondary);
    font-size: 0.8125rem;
    white-space: nowrap;
}

tr:last-child td {
    border-bottom: none;
}

tr:hover td {
    background: var(--hover);
}

/* ========== Badges ========== */

.badge {
    display: inline-block;
    padding: 0.2rem 0.5rem;
    font-size: 0.75rem;
    font-weight: 500;
    border-radius: 4px;
    border: 1px solid var(--border);
    white-space: nowrap;
}

.badge-muted {
    background: transparent;
    color: var(--text-secondary);
}

.badge-default {
    background: var(--secondary);
    color: var(--text);
}

.badge-info {
    background: #1a1a1a;
    color: #ddd;
    border-color: #3a3a3a;
}

.badge-success {
    background: #111;
    color: #fff;
    border-color: #444;
}

.badge-warning {
    background: #1a1a1a;
    color: #ccc;
    border-color: #555;
}

/* ========== Progress bar ========== */

.progress-bar {
    height: 6px;
    background: var(--secondary);
    border-radius: 3px;
    overflow: hidden;
    margin-top: 0.5rem;
}

.progress-fill {
    height: 100%;
    background: var(--text);
    border-radius: 3px;
    transition: width 0.3s ease;
}

.progress-large {
    height: 10px;
    margin: 0.75rem 0;
}

.progress-value {
    font-size: 2rem;
    font-weight: 600;
    letter-spacing: -0.03em;
}

/* ========== Alerts ========== */

.alert {
    padding: 0.875rem 1rem;
    border-radius: var(--radius-sm);
    border: 1px solid var(--border);
    margin-bottom: 1.25rem;
    font-size: 0.875rem;
}

.alert-success {
    background: var(--secondary);
    color: var(--text);
}

.alert-error {
    background: #1a1a1a;
    color: #ddd;
    border-color: #3a3a3a;
}

.alert-info {
    background: var(--secondary);
    color: var(--text-secondary);
}

/* ========== Empty state ========== */

.empty-state {
    text-align: center;
    padding: 3rem 1.5rem;
    color: var(--text-secondary);
}

.empty-state p {
    margin-bottom: 1rem;
}

/* ========== Homepage / Login ========== */

.public-page {
    min-height: 100vh;
    display: flex;
    align-items: center;
    justify-content: center;
    padding: 2rem;
}

.public-card {
    width: 100%;
    max-width: 400px;
    text-align: center;
}

.public-card h1 {
    font-size: 2rem;
    font-weight: 600;
    letter-spacing: -0.03em;
    margin-bottom: 0.5rem;
}

.public-card .tagline {
    color: var(--text-secondary);
    margin-bottom: 2rem;
    font-size: 1rem;
}

.login-form {
    text-align: left;
    background: var(--card);
    border: 1px solid var(--border);
    border-radius: var(--radius);
    padding: 1.75rem;
}

.login-form .form-group:last-of-type {
    margin-bottom: 1.5rem;
}

/* ========== Assignment / Lesson cards ========== */

.item-card {
    background: var(--card);
    border: 1px solid var(--border);
    border-radius: var(--radius);
    padding: 1.25rem;
    display: flex;
    flex-direction: column;
    gap: 0.75rem;
}

.item-card h3 {
    font-size: 1rem;
    font-weight: 600;
}

.item-meta {
    display: flex;
    flex-wrap: wrap;
    gap: 0.75rem;
    font-size: 0.8125rem;
    color: var(--text-secondary);
}

.item-actions {
    display: flex;
    gap: 0.5rem;
    margin-top: auto;
    padding-top: 0.5rem;
}

/* ========== Section ========== */

.section {
    margin-bottom: 2rem;
}

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

.section-title {
    font-size: 1.0625rem;
    font-weight: 600;
}

/* ========== Timeline ========== */

.timeline {
    list-style: none;
    padding: 0;
}

.timeline-item {
    display: flex;
    align-items: flex-start;
    gap: 0.75rem;
    padding: 0.625rem 0;
    border-bottom: 1px solid var(--border);
    font-size: 0.9375rem;
}

.timeline-item:last-child {
    border-bottom: none;
}

.timeline-icon {
    width: 1.25rem;
    text-align: center;
    color: var(--text-secondary);
    flex-shrink: 0;
}

.timeline-item.done .timeline-icon {
    color: var(--text);
}

.timeline-item.current .timeline-icon {
    color: var(--text);
}

/* ========== Detail view ========== */

.detail-header {
    margin-bottom: 1.5rem;
}

.detail-header h2 {
    font-size: 1.375rem;
    font-weight: 600;
    margin-bottom: 0.5rem;
}

.detail-meta {
    display: flex;
    flex-wrap: wrap;
    gap: 1rem;
    font-size: 0.875rem;
    color: var(--text-secondary);
}

.detail-content {
    background: var(--card);
    border: 1px solid var(--border);
    border-radius: var(--radius);
    padding: 1.5rem;
    margin-bottom: 1.5rem;
}

.detail-content h3 {
    font-size: 0.875rem;
    font-weight: 500;
    color: var(--text-secondary);
    margin-bottom: 0.5rem;
    text-transform: uppercase;
    letter-spacing: 0.03em;
}

.detail-content p,
.detail-content pre {
    white-space: pre-wrap;
    word-break: break-word;
}

.detail-content + .detail-content {
    margin-top: 0;
}

/* ========== Submission box ========== */

.submission-box {
    background: var(--secondary);
    border: 1px solid var(--border);
    border-radius: var(--radius);
    padding: 1.25rem;
    margin-top: 1rem;
}

/* ========== Utility ========== */

.text-secondary {
    color: var(--text-secondary);
}

.text-sm {
    font-size: 0.8125rem;
}

.mt-1 { margin-top: 0.5rem; }
.mt-2 { margin-top: 1rem; }
.mt-3 { margin-top: 1.5rem; }
.mb-1 { margin-bottom: 0.5rem; }
.mb-2 { margin-bottom: 1rem; }
.mb-3 { margin-bottom: 1.5rem; }

.flex {
    display: flex;
}

.flex-between {
    display: flex;
    justify-content: space-between;
    align-items: center;
    gap: 1rem;
}

.gap-1 { gap: 0.5rem; }
.gap-2 { gap: 1rem; }

/* ========== Responsive ========== */

@media (max-width: 768px) {
    .sidebar {
        transform: translateX(-100%);
    }
    
    .sidebar.open {
        transform: translateX(0);
    }
    
    .sidebar-overlay.open {
        display: block;
    }
    
    .mobile-menu-btn {
        display: flex;
    }
    
    .main-content {
        margin-left: 0;
    }
    
    .top-header {
        padding: 1rem 1rem 1rem 4rem;
    }
    
    .content-area {
        padding: 1.25rem 1rem 2rem;
    }
    
    .form-row {
        grid-template-columns: 1fr;
    }
    
    .stats-grid {
        grid-template-columns: 1fr 1fr;
    }
    
    .card-grid {
        grid-template-columns: 1fr;
    }
    
    .section-header {
        flex-direction: column;
        align-items: flex-start;
    }
}

@media (max-width: 480px) {
    .stats-grid {
        grid-template-columns: 1fr;
    }
    
    .public-card h1 {
        font-size: 1.75rem;
    }
}