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

:root {
  --bg: #f0f2f5;
  --surface: #ffffff;
  --surface-alt: #f8f9fa;
  --border: #e2e8f0;
  --text-primary: #1a202c;
  --text-secondary: #718096;
  --text-muted: #a0aec0;
  --accent: #6c63ff;
  --accent-hover: #5a52d5;
  --accent-light: #ede9ff;
  --danger: #fc5c7d;
  --danger-hover: #e04368;
  --done-text: #a0aec0;
  --shadow-sm: 0 1px 3px rgba(0,0,0,0.08);
  --shadow-md: 0 4px 16px rgba(0,0,0,0.10);
  --radius: 12px;
  --radius-sm: 8px;
  --transition: 0.2s ease;
}

[data-theme="dark"] {
  --bg: #0f1117;
  --surface: #1a1d27;
  --surface-alt: #22263a;
  --border: #2d3149;
  --text-primary: #e2e8f0;
  --text-secondary: #94a3b8;
  --text-muted: #4a5568;
  --accent: #7c73ff;
  --accent-hover: #6c63ff;
  --accent-light: #1e1b40;
  --danger: #fc5c7d;
  --danger-hover: #ff7a96;
  --done-text: #4a5568;
  --shadow-sm: 0 1px 3px rgba(0,0,0,0.3);
  --shadow-md: 0 4px 20px rgba(0,0,0,0.4);
}

body {
  font-family: 'Inter', -apple-system, BlinkMacSystemFont, 'Segoe UI', sans-serif;
  background: var(--bg);
  color: var(--text-primary);
  min-height: 100vh;
  transition: background var(--transition), color var(--transition);
  display: flex;
  flex-direction: column;
  align-items: center;
  padding: 2rem 1rem 4rem;
}

/* Header */
header {
  width: 100%;
  max-width: 640px;
  display: flex;
  justify-content: space-between;
  align-items: center;
  margin-bottom: 2.5rem;
}

.logo {
  font-size: 1.75rem;
  font-weight: 800;
  letter-spacing: -0.03em;
  color: var(--text-primary);
}

.logo span {
  color: var(--accent);
}

.theme-btn {
  width: 42px;
  height: 42px;
  border-radius: 50%;
  border: 1.5px solid var(--border);
  background: var(--surface);
  color: var(--text-secondary);
  cursor: pointer;
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: 1.1rem;
  transition: background var(--transition), border-color var(--transition), transform var(--transition);
  box-shadow: var(--shadow-sm);
}

.theme-btn:hover {
  background: var(--accent-light);
  border-color: var(--accent);
  color: var(--accent);
  transform: rotate(20deg);
}

/* Input area */
.input-wrapper {
  width: 100%;
  max-width: 640px;
  position: relative;
  margin-bottom: 1.5rem;
}

.task-input {
  width: 100%;
  padding: 1rem 3.5rem 1rem 1.25rem;
  border: 1.5px solid var(--border);
  border-radius: var(--radius);
  background: var(--surface);
  color: var(--text-primary);
  font-size: 1rem;
  outline: none;
  box-shadow: var(--shadow-sm);
  transition: border-color var(--transition), box-shadow var(--transition);
}

.task-input::placeholder {
  color: var(--text-muted);
}

.task-input:focus {
  border-color: var(--accent);
  box-shadow: 0 0 0 3px var(--accent-light), var(--shadow-sm);
}

.add-btn {
  position: absolute;
  right: 10px;
  top: 50%;
  transform: translateY(-50%);
  width: 36px;
  height: 36px;
  border-radius: var(--radius-sm);
  border: none;
  background: var(--accent);
  color: #fff;
  font-size: 1.4rem;
  cursor: pointer;
  display: flex;
  align-items: center;
  justify-content: center;
  transition: background var(--transition), transform var(--transition);
  line-height: 1;
}

.add-btn:hover {
  background: var(--accent-hover);
  transform: translateY(-50%) scale(1.08);
}

/* Card */
.card {
  width: 100%;
  max-width: 640px;
  background: var(--surface);
  border-radius: var(--radius);
  box-shadow: var(--shadow-md);
  overflow: hidden;
  border: 1px solid var(--border);
}

/* Filter tabs */
.filters {
  display: flex;
  border-bottom: 1px solid var(--border);
  padding: 0 1rem;
  gap: 0.25rem;
}

.filter-btn {
  flex: 1;
  padding: 0.85rem 0.5rem;
  border: none;
  background: transparent;
  color: var(--text-secondary);
  font-size: 0.875rem;
  font-weight: 500;
  cursor: pointer;
  border-bottom: 2px solid transparent;
  transition: color var(--transition), border-color var(--transition);
  margin-bottom: -1px;
}

.filter-btn:hover {
  color: var(--accent);
}

.filter-btn.active {
  color: var(--accent);
  border-bottom-color: var(--accent);
  font-weight: 600;
}

/* Task list */
.task-list {
  list-style: none;
  padding: 0.5rem 0;
  min-height: 60px;
}

.task-list:empty::after {
  content: '';
}

.empty-state {
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  padding: 3rem 1rem;
  color: var(--text-muted);
  gap: 0.75rem;
  text-align: center;
}

.empty-state svg {
  opacity: 0.35;
}

.empty-state p {
  font-size: 0.95rem;
}

/* Task item */
.task-item {
  display: flex;
  align-items: center;
  gap: 0.875rem;
  padding: 0.875rem 1.25rem;
  border-bottom: 1px solid var(--border);
  animation: slideIn 0.18s ease;
  transition: background var(--transition);
}

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

.task-item:hover {
  background: var(--surface-alt);
}

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

/* Custom checkbox */
.checkbox {
  flex-shrink: 0;
  width: 22px;
  height: 22px;
  border-radius: 50%;
  border: 2px solid var(--border);
  background: transparent;
  cursor: pointer;
  display: flex;
  align-items: center;
  justify-content: center;
  transition: border-color var(--transition), background var(--transition);
  position: relative;
}

.checkbox:hover {
  border-color: var(--accent);
}

.task-item.done .checkbox {
  border-color: var(--accent);
  background: var(--accent);
}

.checkbox svg {
  display: none;
  color: #fff;
  width: 12px;
  height: 12px;
}

.task-item.done .checkbox svg {
  display: block;
}

/* Task text */
.task-text {
  flex: 1;
  font-size: 0.975rem;
  color: var(--text-primary);
  word-break: break-word;
  transition: color var(--transition);
  cursor: pointer;
  user-select: none;
}

.task-item.done .task-text {
  color: var(--done-text);
  text-decoration: line-through;
  text-decoration-color: var(--text-muted);
}

/* Delete button */
.delete-btn {
  flex-shrink: 0;
  width: 30px;
  height: 30px;
  border-radius: var(--radius-sm);
  border: none;
  background: transparent;
  color: var(--text-muted);
  font-size: 1rem;
  cursor: pointer;
  display: flex;
  align-items: center;
  justify-content: center;
  opacity: 0;
  transition: opacity var(--transition), background var(--transition), color var(--transition);
}

.task-item:hover .delete-btn {
  opacity: 1;
}

.delete-btn:hover {
  background: rgba(252, 92, 125, 0.12);
  color: var(--danger);
}

/* Footer */
.footer {
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: 0.85rem 1.25rem;
  border-top: 1px solid var(--border);
  background: var(--surface-alt);
}

.footer-count {
  font-size: 0.8rem;
  color: var(--text-muted);
}

.clear-btn {
  font-size: 0.8rem;
  color: var(--text-muted);
  border: none;
  background: transparent;
  cursor: pointer;
  padding: 0.25rem 0.5rem;
  border-radius: 4px;
  transition: color var(--transition), background var(--transition);
}

.clear-btn:hover {
  color: var(--danger);
  background: rgba(252, 92, 125, 0.1);
}

/* Removing animation */
.task-item.removing {
  animation: slideOut 0.18s ease forwards;
}

@keyframes slideOut {
  from { opacity: 1; transform: translateX(0); max-height: 60px; }
  to   { opacity: 0; transform: translateX(12px); max-height: 0; padding-top: 0; padding-bottom: 0; }
}

/* Responsive */
@media (max-width: 480px) {
  body { padding: 1.25rem 0.75rem 3rem; }
  .logo { font-size: 1.5rem; }
  .filter-btn { font-size: 0.8rem; }
  .task-item { padding: 0.75rem 1rem; }
  .delete-btn { opacity: 1; }
}