:root {
  --bg: #f6f7fb;
  --card: #ffffff;
  --text: #1f2430;
  --muted: #8a90a0;
  --accent: #4f46e5;
  --accent-dark: #4338ca;
  --danger: #ef4444;
  --border: #e5e7eb;
  --radius: 12px;
  --shadow: 0 10px 30px rgba(31, 36, 48, 0.08);
}

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

body {
  font-family: 'Segoe UI', system-ui, -apple-system, Arial, sans-serif;
  background: var(--bg);
  color: var(--text);
  min-height: 100vh;
  display: flex;
  align-items: flex-start;
  justify-content: center;
  padding: 48px 16px;
}

.app {
  width: 100%;
  max-width: 560px;
  background: var(--card);
  border-radius: var(--radius);
  box-shadow: var(--shadow);
  padding: 32px;
}

.app-header {
  text-align: center;
  margin-bottom: 24px;
}

.app-header h1 {
  font-size: 1.75rem;
  font-weight: 700;
  letter-spacing: -0.02em;
}

.subtitle {
  color: var(--muted);
  font-size: 0.9rem;
  margin-top: 6px;
}

.todo-form {
  display: flex;
  gap: 10px;
  margin-bottom: 20px;
}

.todo-form input {
  flex: 1;
  padding: 12px 14px;
  border: 1px solid var(--border);
  border-radius: 8px;
  font-size: 1rem;
  outline: none;
  transition: border-color 0.15s, box-shadow 0.15s;
}

.todo-form input:focus {
  border-color: var(--accent);
  box-shadow: 0 0 0 3px rgba(79, 70, 229, 0.15);
}

.btn-add {
  padding: 12px 18px;
  background: var(--accent);
  color: #fff;
  border: none;
  border-radius: 8px;
  font-size: 0.95rem;
  font-weight: 600;
  cursor: pointer;
  transition: background 0.15s;
  white-space: nowrap;
}

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

.btn-add:disabled {
  opacity: 0.6;
  cursor: not-allowed;
}

.todo-list {
  list-style: none;
}

.todo-item {
  display: flex;
  align-items: center;
  gap: 12px;
  padding: 12px 6px;
  border-bottom: 1px solid var(--border);
  animation: fadeIn 0.2s ease;
}

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

.todo-item input[type='checkbox'] {
  width: 18px;
  height: 18px;
  accent-color: var(--accent);
  cursor: pointer;
  flex-shrink: 0;
}

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

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

.todo-delete {
  background: none;
  border: none;
  color: var(--muted);
  font-size: 1.1rem;
  cursor: pointer;
  padding: 4px 8px;
  border-radius: 6px;
  transition: color 0.15s, background 0.15s;
  flex-shrink: 0;
}

.todo-delete:hover {
  color: var(--danger);
  background: rgba(239, 68, 68, 0.08);
}

.app-footer {
  display: flex;
  justify-content: space-between;
  align-items: center;
  margin-top: 16px;
  color: var(--muted);
  font-size: 0.85rem;
}

.btn-clear {
  background: none;
  border: 1px solid var(--border);
  color: var(--muted);
  padding: 6px 12px;
  border-radius: 8px;
  font-size: 0.85rem;
  cursor: pointer;
  transition: color 0.15s, border-color 0.15s;
}

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

.empty-state {
  text-align: center;
  color: var(--muted);
  padding: 24px 0;
  font-size: 0.95rem;
}

@keyframes fadeIn {
  from {
    opacity: 0;
    transform: translateY(-4px);
  }
  to {
    opacity: 1;
    transform: translateY(0);
  }
}

@media (max-width: 480px) {
  body {
    padding: 24px 12px;
  }
  .app {
    padding: 20px;
  }
}