/* ================================================================
   Student Task Manager — Modern Dashboard Styles
   ================================================================ */

:root {
  --primary: #6366f1;
  --primary-hover: #4f46e5;
  --primary-soft: #eef2ff;
  --danger: #ef4444;
  --danger-soft: #fef2f2;
  --success: #10b981;
  --success-soft: #ecfdf5;
  --warning: #f59e0b;
  --warning-soft: #fffbeb;

  --bg: #f5f7fb;
  --surface: #ffffff;
  --surface-2: #f8fafc;
  --border: #e5e7eb;
  --border-strong: #d1d5db;

  --text: #0f172a;
  --text-2: #475569;
  --text-3: #94a3b8;

  --radius-sm: 8px;
  --radius: 14px;
  --radius-lg: 20px;
  --radius-xl: 28px;

  --shadow-xs: 0 1px 2px rgba(15,23,42,0.04);
  --shadow-sm: 0 2px 6px rgba(15,23,42,0.06);
  --shadow: 0 4px 16px rgba(15,23,42,0.08);
  --shadow-lg: 0 20px 40px -12px rgba(15,23,42,0.18);
  --shadow-primary: 0 8px 24px -6px rgba(99,102,241,0.5);

  --transition: 180ms cubic-bezier(0.4, 0, 0.2, 1);
}

[data-theme="dark"] {
  --primary: #818cf8;
  --primary-hover: #6366f1;
  --primary-soft: #1e1b4b;

  --bg: #0b1120;
  --surface: #111827;
  --surface-2: #1e293b;
  --border: #1f2937;
  --border-strong: #374151;

  --text: #f1f5f9;
  --text-2: #cbd5e1;
  --text-3: #64748b;

  --shadow-xs: 0 1px 2px rgba(0,0,0,0.3);
  --shadow-sm: 0 2px 6px rgba(0,0,0,0.4);
  --shadow: 0 4px 16px rgba(0,0,0,0.5);
  --shadow-lg: 0 20px 40px -12px rgba(0,0,0,0.7);
  --shadow-primary: 0 8px 24px -6px rgba(99,102,241,0.5);

  --danger-soft: #3f1d1d;
  --success-soft: #0d2818;
  --warning-soft: #3a2a0d;
}

* { margin: 0; padding: 0; box-sizing: border-box; }
*:focus-visible { outline: 2px solid var(--primary); outline-offset: 2px; border-radius: 6px; }

html, body { height: 100%; }

body {
  font-family: 'Inter', system-ui, -apple-system, sans-serif;
  background: var(--bg);
  color: var(--text);
  font-size: 14px;
  line-height: 1.5;
  -webkit-font-smoothing: antialiased;
  transition: background-color 300ms, color 300ms;
}

/* ================================================================
   Layout
   ================================================================ */
.app { display: flex; min-height: 100vh; }

/* ================================================================
   Sidebar
   ================================================================ */
.sidebar {
  width: 260px;
  background: var(--surface);
  border-right: 1px solid var(--border);
  padding: 1.5rem 1.25rem;
  display: flex;
  flex-direction: column;
  position: fixed;
  height: 100vh;
  overflow-y: auto;
  z-index: 50;
  transition: transform var(--transition), background-color 300ms;
}

.sidebar-header {
  display: flex;
  align-items: center;
  justify-content: space-between;
  margin-bottom: 2rem;
  gap: 0.5rem;
}

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

.logo-mark {
  width: 40px; height: 40px;
  background: linear-gradient(135deg, #6366f1, #8b5cf6);
  border-radius: 12px;
  display: flex; align-items: center; justify-content: center;
  font-size: 1.25rem;
  box-shadow: 0 6px 16px -4px rgba(99,102,241,0.5);
  flex-shrink: 0;
}

.logo-text { display: flex; flex-direction: column; line-height: 1.15; }
.logo-title { font-weight: 700; font-size: 0.95rem; color: var(--text); }
.logo-subtitle { font-size: 0.7rem; color: var(--text-3); font-weight: 500; }

.theme-toggle {
  background: var(--surface-2);
  border: 1px solid var(--border);
  width: 34px; height: 34px;
  border-radius: 10px;
  display: flex; align-items: center; justify-content: center;
  cursor: pointer;
  color: var(--text-2);
  transition: all var(--transition);
  flex-shrink: 0;
}
.theme-toggle:hover { color: var(--primary); border-color: var(--primary); transform: rotate(15deg); }
[data-theme="dark"] .icon-sun { display: none; }
[data-theme="light"] .icon-moon, :root:not([data-theme="dark"]) .icon-moon { display: none; }
[data-theme="dark"] .icon-moon { display: block; }

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

.nav-item {
  display: flex; align-items: center; gap: 0.75rem;
  padding: 0.7rem 0.9rem;
  border-radius: 10px;
  text-decoration: none;
  color: var(--text-2);
  font-weight: 500;
  font-size: 0.875rem;
  transition: all var(--transition);
}
.nav-item:hover { background: var(--surface-2); color: var(--text); }
.nav-item.active {
  background: linear-gradient(135deg, #6366f1, #8b5cf6);
  color: white;
  box-shadow: 0 6px 16px -6px rgba(99,102,241,0.6);
}

.sidebar-footer { margin-top: auto; padding-top: 1.5rem; }

.progress-widget {
  background: var(--surface-2);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 1rem;
  display: flex;
  align-items: center;
  gap: 0.75rem;
}

.progress-ring-wrap { position: relative; width: 80px; height: 80px; flex-shrink: 0; }

.progress-ring { transform: rotate(-90deg); }
.ring-bg { stroke: var(--border); }
.ring-fill {
  stroke: url(#grad) var(--primary);
  stroke: var(--primary);
  stroke-dasharray: 213.6;
  stroke-dashoffset: 213.6;
  transition: stroke-dashoffset 800ms cubic-bezier(0.4, 0, 0.2, 1);
}

.ring-label {
  position: absolute; inset: 0;
  display: flex; align-items: center; justify-content: center;
  font-weight: 700; font-size: 0.9rem; color: var(--text);
}

.progress-text { display: flex; flex-direction: column; min-width: 0; }
.progress-title { font-weight: 600; font-size: 0.8rem; color: var(--text); }
.progress-sub { font-size: 0.7rem; color: var(--text-3); }

/* ================================================================
   Overlay (mobile)
   ================================================================ */
.overlay {
  position: fixed; inset: 0;
  background: rgba(15,23,42,0.5);
  backdrop-filter: blur(4px);
  opacity: 0; pointer-events: none;
  transition: opacity var(--transition);
  z-index: 40;
}
.overlay.show { opacity: 1; pointer-events: auto; }

/* ================================================================
   Main Content
   ================================================================ */
.main {
  flex: 1;
  margin-left: 260px;
  padding: 2rem 2.5rem;
  max-width: 1400px;
  width: 100%;
}

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

.menu-btn {
  display: none;
  background: var(--surface);
  border: 1px solid var(--border);
  width: 40px; height: 40px;
  border-radius: 10px;
  cursor: pointer;
  color: var(--text);
  align-items: center; justify-content: center;
}

.topbar-title { flex: 1; min-width: 0; }
.topbar-title h1 {
  font-size: 1.75rem;
  font-weight: 800;
  letter-spacing: -0.02em;
  color: var(--text);
  line-height: 1.2;
}
.topbar-sub { font-size: 0.85rem; color: var(--text-3); margin-top: 0.15rem; }

/* ================================================================
   Buttons
   ================================================================ */
.btn {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: 0.5rem;
  padding: 0.65rem 1.15rem;
  border-radius: 10px;
  font-family: inherit;
  font-weight: 600;
  font-size: 0.85rem;
  border: 1px solid transparent;
  cursor: pointer;
  transition: all var(--transition);
  white-space: nowrap;
  text-decoration: none;
}

.btn-primary {
  background: linear-gradient(135deg, #6366f1, #8b5cf6);
  color: white;
  box-shadow: var(--shadow-primary);
}
.btn-primary:hover { transform: translateY(-1px); box-shadow: 0 12px 28px -6px rgba(99,102,241,0.55); }
.btn-primary:active { transform: translateY(0); }

.btn-ghost {
  background: var(--surface);
  border-color: var(--border);
  color: var(--text-2);
}
.btn-ghost:hover { background: var(--surface-2); color: var(--text); border-color: var(--border-strong); }

.btn-danger {
  background: var(--danger);
  color: white;
  box-shadow: 0 6px 16px -4px rgba(239,68,68,0.5);
}
.btn-danger:hover { background: #dc2626; transform: translateY(-1px); }

.btn-add { padding: 0.7rem 1.25rem; }

.icon-btn {
  background: transparent;
  border: none;
  color: var(--text-3);
  width: 32px; height: 32px;
  border-radius: 8px;
  cursor: pointer;
  display: flex; align-items: center; justify-content: center;
  transition: all var(--transition);
}
.icon-btn:hover { background: var(--surface-2); color: var(--text); }

/* ================================================================
   Stats Grid
   ================================================================ */
.stats-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(180px, 1fr));
  gap: 1rem;
  margin-bottom: 2rem;
}

.stat-card {
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 1.15rem 1.25rem;
  display: flex;
  align-items: center;
  gap: 0.9rem;
  box-shadow: var(--shadow-xs);
  transition: all var(--transition);
  position: relative;
  overflow: hidden;
}
.stat-card:hover { transform: translateY(-2px); box-shadow: var(--shadow); border-color: var(--border-strong); }

.stat-card::before {
  content: '';
  position: absolute;
  left: 0; top: 0; bottom: 0;
  width: 3px;
  background: var(--primary);
  opacity: 0;
  transition: opacity var(--transition);
}
.stat-card:hover::before { opacity: 1; }

.stat-icon {
  width: 42px; height: 42px;
  border-radius: 12px;
  display: flex; align-items: center; justify-content: center;
  background: var(--primary-soft);
  color: var(--primary);
  flex-shrink: 0;
}

.stat-info { display: flex; flex-direction: column; min-width: 0; }
.stat-label { font-size: 0.72rem; color: var(--text-3); font-weight: 600; text-transform: uppercase; letter-spacing: 0.04em; }
.stat-value { font-size: 1.65rem; font-weight: 800; color: var(--text); line-height: 1.1; letter-spacing: -0.02em; }

.stat-card[data-accent="pending"] .stat-icon { background: var(--warning-soft); color: var(--warning); }
.stat-card[data-accent="progress"] .stat-icon { background: var(--primary-soft); color: var(--primary); }
.stat-card[data-accent="completed"] .stat-icon { background: var(--success-soft); color: var(--success); }
.stat-card[data-accent="high"] .stat-icon { background: var(--danger-soft); color: var(--danger); }

/* ================================================================
   Toolbar / Filters
   ================================================================ */
.toolbar {
  display: flex;
  gap: 0.65rem;
  margin-bottom: 1.5rem;
  flex-wrap: wrap;
  align-items: center;
}

.search-wrap {
  position: relative;
  flex: 1;
  min-width: 220px;
}

.search-icon {
  position: absolute;
  left: 0.9rem; top: 50%;
  transform: translateY(-50%);
  color: var(--text-3);
  pointer-events: none;
}

.search-wrap input {
  width: 100%;
  padding: 0.7rem 0.9rem 0.7rem 2.5rem;
  border: 1px solid var(--border);
  border-radius: 10px;
  background: var(--surface);
  font-family: inherit;
  font-size: 0.85rem;
  color: var(--text);
  transition: all var(--transition);
}
.search-wrap input:focus {
  outline: none;
  border-color: var(--primary);
  box-shadow: 0 0 0 4px var(--primary-soft);
}
.search-wrap input::placeholder { color: var(--text-3); }

.toolbar select {
  padding: 0.7rem 0.9rem;
  border: 1px solid var(--border);
  border-radius: 10px;
  background: var(--surface);
  font-family: inherit;
  font-size: 0.85rem;
  color: var(--text);
  cursor: pointer;
  transition: all var(--transition);
  appearance: none;
  padding-right: 2.2rem;
  background-image: url("data:image/svg+xml,%3Csvg xmlns='http://www.w3.org/2000/svg' width='16' height='16' viewBox='0 0 24 24' fill='none' stroke='%2394a3b8' stroke-width='2' stroke-linecap='round'%3E%3Cpath d='M6 9l6 6 6-6'/%3E%3C/svg%3E");
  background-repeat: no-repeat;
  background-position: right 0.75rem center;
}
.toolbar select:focus {
  outline: none;
  border-color: var(--primary);
  box-shadow: 0 0 0 4px var(--primary-soft);
}

/* ================================================================
   Task List
   ================================================================ */
.task-list {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(320px, 1fr));
  gap: 1rem;
}

.task-card {
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 1.25rem;
  display: flex;
  flex-direction: column;
  gap: 0.85rem;
  box-shadow: var(--shadow-xs);
  transition: all var(--transition);
  position: relative;
  overflow: hidden;
  animation: fadeInUp 320ms cubic-bezier(0.4, 0, 0.2, 1) backwards;
}

@keyframes fadeInUp {
  from { opacity: 0; transform: translateY(8px); }
  to { opacity: 1; transform: translateY(0); }
}

.task-card::before {
  content: '';
  position: absolute;
  left: 0; top: 0; bottom: 0;
  width: 4px;
  background: var(--border);
  transition: all var(--transition);
}

.task-card[data-priority="Low"]::before { background: var(--success); }
.task-card[data-priority="Medium"]::before { background: var(--warning); }
.task-card[data-priority="High"]::before { background: var(--danger); }

.task-card:hover { box-shadow: var(--shadow); transform: translateY(-2px); border-color: var(--border-strong); }
.task-card[data-status="Completed"] { opacity: 0.75; }
.task-card[data-status="Completed"] .task-card-title { text-decoration: line-through; color: var(--text-3); }

.task-card-header {
  display: flex;
  align-items: flex-start;
  justify-content: space-between;
  gap: 0.5rem;
}

.task-card-title {
  font-weight: 700;
  font-size: 0.98rem;
  color: var(--text);
  line-height: 1.35;
  word-break: break-word;
}

.task-badge {
  font-size: 0.65rem;
  font-weight: 700;
  padding: 0.25rem 0.6rem;
  border-radius: 999px;
  text-transform: uppercase;
  letter-spacing: 0.05em;
  flex-shrink: 0;
}
.task-badge[data-priority="High"] { background: var(--danger-soft); color: var(--danger); }
.task-badge[data-priority="Medium"] { background: var(--warning-soft); color: #b45309; }
.task-badge[data-priority="Low"] { background: var(--success-soft); color: #047857; }
[data-theme="dark"] .task-badge[data-priority="Medium"] { color: #fbbf24; }
[data-theme="dark"] .task-badge[data-priority="Low"] { color: #34d399; }

.task-description {
  font-size: 0.85rem;
  color: var(--text-2);
  line-height: 1.55;
  display: -webkit-box;
  -webkit-line-clamp: 2;
  -webkit-box-orient: vertical;
  overflow: hidden;
}

.task-status {
  display: inline-flex;
  align-items: center;
  gap: 0.4rem;
  font-size: 0.75rem;
  font-weight: 600;
  padding: 0.3rem 0.7rem;
  border-radius: 999px;
  width: fit-content;
}
.task-status::before {
  content: '';
  width: 6px; height: 6px;
  border-radius: 50%;
  background: currentColor;
}
.task-status[data-status="Pending"] { background: var(--warning-soft); color: #b45309; }
.task-status[data-status="In Progress"] { background: var(--primary-soft); color: var(--primary); }
.task-status[data-status="Completed"] { background: var(--success-soft); color: #047857; }
[data-theme="dark"] .task-status[data-status="Pending"] { color: #fbbf24; }
[data-theme="dark"] .task-status[data-status="Completed"] { color: #34d399; }

.task-meta {
  display: flex;
  flex-wrap: wrap;
  gap: 0.9rem;
  font-size: 0.72rem;
  color: var(--text-3);
  font-weight: 500;
}
.task-meta span { display: inline-flex; align-items: center; gap: 0.35rem; }

.task-actions {
  display: flex;
  gap: 0.5rem;
  margin-top: auto;
  padding-top: 0.85rem;
  border-top: 1px solid var(--border);
}
.task-actions .btn { padding: 0.45rem 0.85rem; font-size: 0.78rem; }

/* ================================================================
   Empty State
   ================================================================ */
.empty-state {
  grid-column: 1 / -1;
  text-align: center;
  padding: 4rem 2rem;
  background: var(--surface);
  border: 2px dashed var(--border);
  border-radius: var(--radius-lg);
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: 0.75rem;
}
.empty-illustration { color: var(--text-3); opacity: 0.6; margin-bottom: 0.5rem; }
.empty-state h3 { font-size: 1.15rem; font-weight: 700; color: var(--text); }
.empty-state p { font-size: 0.9rem; color: var(--text-3); }

/* ================================================================
   Modals
   ================================================================ */
.modal-overlay {
  position: fixed; inset: 0;
  background: rgba(15,23,42,0.5);
  backdrop-filter: blur(6px);
  display: flex;
  align-items: center;
  justify-content: center;
  z-index: 100;
  padding: 1rem;
  opacity: 0;
  pointer-events: none;
  transition: opacity 200ms;
}
.modal-overlay.active { opacity: 1; pointer-events: auto; }

.modal {
  background: var(--surface);
  border-radius: var(--radius-lg);
  padding: 1.75rem;
  width: 100%;
  max-width: 500px;
  box-shadow: var(--shadow-lg);
  max-height: 90vh;
  overflow-y: auto;
  transform: scale(0.96) translateY(10px);
  transition: transform 250ms cubic-bezier(0.4, 0, 0.2, 1);
}
.modal-overlay.active .modal { transform: scale(1) translateY(0); }

.modal-sm { max-width: 400px; text-align: center; }
.modal-sm .modal-actions { justify-content: center; }

.modal-header {
  display: flex;
  align-items: center;
  justify-content: space-between;
  margin-bottom: 1.5rem;
}
.modal h2 { font-size: 1.2rem; font-weight: 700; letter-spacing: -0.01em; }
.modal-sm h2 { text-align: center; margin-bottom: 0.5rem; }
.modal-text { font-size: 0.88rem; color: var(--text-2); margin-bottom: 1.5rem; line-height: 1.5; }

.modal-icon {
  width: 56px; height: 56px;
  border-radius: 50%;
  display: flex; align-items: center; justify-content: center;
  margin: 0 auto 1rem;
}
.modal-icon.danger { background: var(--danger-soft); color: var(--danger); }

/* ================================================================
   Forms
   ================================================================ */
.form-group { margin-bottom: 1.1rem; }
.form-group label {
  display: block;
  font-size: 0.82rem;
  font-weight: 600;
  color: var(--text-2);
  margin-bottom: 0.45rem;
}
.required { color: var(--danger); }

.form-group input,
.form-group select,
.form-group textarea {
  width: 100%;
  padding: 0.7rem 0.9rem;
  border: 1px solid var(--border);
  border-radius: 10px;
  background: var(--surface);
  font-family: inherit;
  font-size: 0.88rem;
  color: var(--text);
  transition: all var(--transition);
  resize: vertical;
}
.form-group input:focus,
.form-group select:focus,
.form-group textarea:focus {
  outline: none;
  border-color: var(--primary);
  box-shadow: 0 0 0 4px var(--primary-soft);
}
.form-group input::placeholder,
.form-group textarea::placeholder { color: var(--text-3); }

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

.modal-actions {
  display: flex;
  justify-content: flex-end;
  gap: 0.65rem;
  margin-top: 1.5rem;
}

/* ================================================================
   Toast Notifications
   ================================================================ */
.toast-container {
  position: fixed;
  bottom: 1.5rem;
  right: 1.5rem;
  display: flex;
  flex-direction: column;
  gap: 0.6rem;
  z-index: 200;
  pointer-events: none;
}

.toast {
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 0.85rem 1.1rem;
  box-shadow: var(--shadow-lg);
  display: flex;
  align-items: center;
  gap: 0.75rem;
  font-size: 0.86rem;
  font-weight: 500;
  color: var(--text);
  min-width: 260px;
  max-width: 380px;
  pointer-events: auto;
  animation: slideInRight 300ms cubic-bezier(0.4, 0, 0.2, 1);
  border-left: 3px solid var(--primary);
}
.toast.success { border-left-color: var(--success); }
.toast.error { border-left-color: var(--danger); }

.toast-icon {
  width: 28px; height: 28px;
  border-radius: 50%;
  display: flex; align-items: center; justify-content: center;
  flex-shrink: 0;
  background: var(--primary-soft);
  color: var(--primary);
}
.toast.success .toast-icon { background: var(--success-soft); color: var(--success); }
.toast.error .toast-icon { background: var(--danger-soft); color: var(--danger); }

@keyframes slideInRight {
  from { opacity: 0; transform: translateX(40px); }
  to { opacity: 1; transform: translateX(0); }
}
.toast.leaving { animation: slideOutRight 250ms forwards; }
@keyframes slideOutRight {
  to { opacity: 0; transform: translateX(40px); }
}

/* ================================================================
   Responsive
   ================================================================ */
@media (max-width: 900px) {
  .sidebar { transform: translateX(-100%); }
  .sidebar.open { transform: translateX(0); box-shadow: var(--shadow-lg); }
  .main { margin-left: 0; padding: 1.25rem 1.25rem 2rem; }
  .menu-btn { display: flex; }
  .topbar-title h1 { font-size: 1.4rem; }
  .topbar-sub { display: none; }
}

@media (max-width: 640px) {
  .stats-grid { grid-template-columns: repeat(2, 1fr); }
  .task-list { grid-template-columns: 1fr; }
  .toolbar { flex-direction: column; align-items: stretch; }
  .toolbar select, .search-wrap { width: 100%; }
  .form-row { grid-template-columns: 1fr; }
  .btn-add span { display: none; }
  .btn-add { padding: 0.7rem; }
  .toast-container { left: 1rem; right: 1rem; bottom: 1rem; }
  .toast { min-width: 0; width: 100%; }
}