:root {
  --bg: #f4f6f9;
  --surface: #ffffff;
  --text: #1a1d23;
  --text-muted: #6b7280;
  --border: #e5e7eb;
  --accent: #4f46e5;
  --accent-hover: #4338ca;
  --danger: #ef4444;
  --success: #10b981;
  --shadow: 0 2px 8px rgba(0, 0, 0, 0.06);
  --high: #dc2626;
  --medium: #d97706;
  --low: #16a34a;
}

[data-theme="dark"] {
  --bg: #111827;
  --surface: #1f2937;
  --text: #f9fafb;
  --text-muted: #9ca3af;
  --border: #374151;
  --accent: #818cf8;
  --accent-hover: #6366f1;
  --shadow: 0 2px 8px rgba(0, 0, 0, 0.4);
}

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

body {
  font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, "PingFang SC",
    "Microsoft YaHei", sans-serif;
  background: var(--bg);
  color: var(--text);
  min-height: 100vh;
  transition: background 0.3s, color 0.3s;
}

.app {
  max-width: 720px;
  margin: 0 auto;
  padding: 24px 16px 60px;
}

.app-header {
  display: flex;
  align-items: center;
  justify-content: space-between;
  margin-bottom: 20px;
}

.app-header h1 {
  font-size: 1.8rem;
  font-weight: 700;
  letter-spacing: -0.5px;
}

.icon-btn {
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: 10px;
  padding: 8px 10px;
  font-size: 1.2rem;
  cursor: pointer;
  transition: transform 0.2s;
}

.icon-btn:hover {
  transform: scale(1.08);
}

.stats-bar {
  display: flex;
  gap: 12px;
  margin-bottom: 20px;
}

.stat {
  flex: 1;
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: 12px;
  padding: 14px;
  text-align: center;
  box-shadow: var(--shadow);
}

.stat span {
  display: block;
  font-size: 1.6rem;
  font-weight: 700;
  color: var(--accent);
}

.stat label {
  font-size: 0.85rem;
  color: var(--text-muted);
}

.add-form {
  display: flex;
  flex-wrap: wrap;
  gap: 8px;
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: 12px;
  padding: 12px;
  margin-bottom: 16px;
  box-shadow: var(--shadow);
}

.add-form input[type="text"] {
  flex: 1 1 100%;
  border: 1px solid var(--border);
  background: var(--bg);
  color: var(--text);
  border-radius: 8px;
  padding: 10px 12px;
  font-size: 1rem;
  outline: none;
}

.add-form input:focus,
.add-form select:focus {
  border-color: var(--accent);
}

.add-form select {
  flex: 1;
  border: 1px solid var(--border);
  background: var(--bg);
  color: var(--text);
  border-radius: 8px;
  padding: 10px;
  outline: none;
}

.btn-add {
  background: var(--accent);
  color: #fff;
  border: none;
  border-radius: 8px;
  padding: 10px 20px;
  font-size: 1rem;
  font-weight: 600;
  cursor: pointer;
}

.btn-add:hover {
  background: var(--accent-hover);
}

.filters {
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  gap: 10px;
  margin-bottom: 16px;
}

.filter-group {
  display: flex;
  gap: 6px;
  flex-wrap: wrap;
  flex: 1;
}

.filter-btn {
  background: var(--surface);
  border: 1px solid var(--border);
  color: var(--text-muted);
  border-radius: 20px;
  padding: 6px 14px;
  cursor: pointer;
  font-size: 0.9rem;
  transition: all 0.2s;
}

.filter-btn.active {
  background: var(--accent);
  color: #fff;
  border-color: var(--accent);
}

.filter-select,
#searchInput {
  border: 1px solid var(--border);
  background: var(--surface);
  color: var(--text);
  border-radius: 8px;
  padding: 7px 10px;
  font-size: 0.9rem;
  outline: none;
}

#searchInput {
  flex: 1;
  min-width: 120px;
}

.btn-clear {
  background: transparent;
  border: 1px solid var(--danger);
  color: var(--danger);
  border-radius: 8px;
  padding: 7px 14px;
  cursor: pointer;
  font-size: 0.9rem;
}

.btn-clear:hover {
  background: var(--danger);
  color: #fff;
}

.todo-list {
  list-style: none;
  display: flex;
  flex-direction: column;
  gap: 10px;
}

.todo-item {
  display: flex;
  align-items: flex-start;
  gap: 12px;
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: 12px;
  padding: 14px;
  box-shadow: var(--shadow);
  animation: fadeIn 0.25s ease;
}

@keyframes fadeIn {
  from { opacity: 0; transform: translateY(-6px); }
  to { opacity: 1; transform: translateY(0); }
}

.todo-checkbox {
  width: 22px;
  height: 22px;
  flex-shrink: 0;
  accent-color: var(--accent);
  cursor: pointer;
  margin-top: 3px;
}

.todo-body {
  flex: 1;
  min-width: 0;
}

.todo-title {
  font-size: 1rem;
  font-weight: 500;
  word-break: break-word;
}

.todo-item.completed .todo-title {
  text-decoration: line-through;
  color: var(--text-muted);
}

.todo-description {
  font-size: 0.85rem;
  color: var(--text-muted);
  margin-top: 4px;
  word-break: break-word;
}

.todo-meta {
  display: flex;
  gap: 6px;
  margin-top: 8px;
  flex-wrap: wrap;
}

.tag {
  font-size: 0.72rem;
  padding: 3px 8px;
  border-radius: 10px;
  font-weight: 500;
}

.tag-priority.high { background: rgba(220, 38, 38, 0.15); color: var(--high); }
.tag-priority.medium { background: rgba(217, 119, 6, 0.15); color: var(--medium); }
.tag-priority.low { background: rgba(22, 163, 74, 0.15); color: var(--low); }

.tag-category {
  background: rgba(79, 70, 229, 0.1);
  color: var(--accent);
}

.todo-time {
  font-size: 0.72rem;
  color: var(--text-muted);
}

.todo-actions {
  display: flex;
  gap: 6px;
  flex-shrink: 0;
}

.action-btn {
  background: transparent;
  border: 1px solid var(--border);
  border-radius: 8px;
  padding: 6px 10px;
  cursor: pointer;
  color: var(--text-muted);
  font-size: 0.85rem;
  transition: all 0.2s;
}

.action-btn.edit:hover {
  border-color: var(--accent);
  color: var(--accent);
}

.action-btn.delete:hover {
  border-color: var(--danger);
  color: var(--danger);
}

.empty-state {
  text-align: center;
  color: var(--text-muted);
  padding: 60px 0;
  font-size: 1.1rem;
}

.modal-overlay {
  position: fixed;
  inset: 0;
  background: rgba(0, 0, 0, 0.5);
  display: flex;
  align-items: center;
  justify-content: center;
  z-index: 100;
  backdrop-filter: blur(2px);
}

.modal {
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: 16px;
  padding: 24px;
  width: 90%;
  max-width: 440px;
  box-shadow: 0 20px 50px rgba(0, 0, 0, 0.2);
}

.modal h2 {
  margin-bottom: 16px;
  font-size: 1.3rem;
}

.modal label {
  display: block;
  font-size: 0.85rem;
  color: var(--text-muted);
  margin: 12px 0 4px;
}

.modal input,
.modal select {
  width: 100%;
  border: 1px solid var(--border);
  background: var(--bg);
  color: var(--text);
  border-radius: 8px;
  padding: 9px 12px;
  font-size: 1rem;
  outline: none;
}

.modal input:focus,
.modal select:focus {
  border-color: var(--accent);
}

.modal-actions {
  display: flex;
  justify-content: flex-end;
  gap: 10px;
  margin-top: 20px;
}

.btn-cancel {
  background: transparent;
  border: 1px solid var(--border);
  color: var(--text-muted);
  border-radius: 8px;
  padding: 9px 18px;
  cursor: pointer;
}

.toast {
  position: fixed;
  bottom: 24px;
  left: 50%;
  transform: translateX(-50%);
  background: var(--text);
  color: var(--bg);
  padding: 10px 20px;
  border-radius: 8px;
  font-size: 0.9rem;
  box-shadow: var(--shadow);
  z-index: 200;
  animation: fadeIn 0.2s ease;
}

@media (max-width: 560px) {
  .filters {
    flex-direction: column;
  }
}