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

:root {
  --bg: #0f0f13;
  --surface: #1a1a22;
  --surface-hover: #22222c;
  --border: #2a2a36;
  --text: #f0f0f5;
  --text-muted: #8888a0;
  --accent: #6366f1;
  --accent-hover: #818cf8;
  --accent-glow: rgba(99, 102, 241, 0.25);
  --success: #34d399;
  --danger: #f87171;
  --radius: 12px;
  --radius-sm: 8px;
  --shadow: 0 4px 24px rgba(0, 0, 0, 0.4);
  --transition: 150ms ease;
}

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

body {
  font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, "Helvetica Neue", sans-serif;
  background: var(--bg);
  color: var(--text);
  min-height: 100dvh;
  line-height: 1.5;
  -webkit-font-smoothing: antialiased;
}

.app {
  max-width: 520px;
  margin: 0 auto;
  padding: 2rem 1.25rem 3rem;
}

/* Header */

.header {
  margin-bottom: 2rem;
}

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

.title {
  font-size: 2rem;
  font-weight: 700;
  letter-spacing: -0.03em;
  background: linear-gradient(135deg, var(--text) 0%, var(--accent-hover) 100%);
  -webkit-background-clip: text;
  -webkit-text-fill-color: transparent;
  background-clip: text;
}

.subtitle {
  margin-top: 0.35rem;
  font-size: 0.875rem;
  color: var(--text-muted);
}

.status {
  display: flex;
  align-items: center;
  gap: 0.4rem;
  font-size: 0.75rem;
  color: var(--text-muted);
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: 999px;
  padding: 0.3rem 0.75rem;
  white-space: nowrap;
}

.status-dot {
  width: 7px;
  height: 7px;
  border-radius: 50%;
  background: var(--success);
  flex-shrink: 0;
}

.status.offline .status-dot {
  background: var(--text-muted);
}

/* Add form */

.add-form {
  display: flex;
  gap: 0.5rem;
  margin-bottom: 1.25rem;
}

.todo-input {
  flex: 1;
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  color: var(--text);
  font-size: 1rem;
  padding: 0.85rem 1rem;
  outline: none;
  transition: border-color var(--transition), box-shadow var(--transition);
}

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

.todo-input:focus {
  border-color: var(--accent);
  box-shadow: 0 0 0 3px var(--accent-glow);
}

.btn-add {
  display: flex;
  align-items: center;
  justify-content: center;
  width: 48px;
  height: 48px;
  background: var(--accent);
  border: none;
  border-radius: var(--radius);
  color: white;
  cursor: pointer;
  flex-shrink: 0;
  transition: background var(--transition), transform var(--transition);
}

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

.btn-add:active {
  transform: scale(0.95);
}

/* Filters */

.filters {
  display: flex;
  gap: 0.25rem;
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 0.25rem;
  margin-bottom: 1rem;
}

.filter-btn {
  flex: 1;
  background: transparent;
  border: none;
  border-radius: var(--radius-sm);
  color: var(--text-muted);
  cursor: pointer;
  font-size: 0.875rem;
  font-weight: 500;
  padding: 0.5rem;
  transition: background var(--transition), color var(--transition);
}

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

.filter-btn.active {
  background: var(--accent);
  color: white;
}

/* Todo list */

.todo-list {
  list-style: none;
  display: flex;
  flex-direction: column;
  gap: 0.5rem;
}

.todo-item {
  display: flex;
  align-items: center;
  gap: 0.75rem;
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 0.75rem 1rem;
  transition: background var(--transition), border-color var(--transition), opacity var(--transition);
  animation: slideIn 200ms ease;
}

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

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

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

.todo-item.completed {
  opacity: 0.7;
}

/* Custom checkbox */

.todo-check {
  position: relative;
  display: flex;
  align-items: center;
  cursor: pointer;
  flex-shrink: 0;
}

.todo-checkbox {
  position: absolute;
  opacity: 0;
  width: 0;
  height: 0;
}

.checkmark {
  display: block;
  width: 22px;
  height: 22px;
  border: 2px solid var(--border);
  border-radius: 50%;
  transition: border-color var(--transition), background var(--transition);
}

.todo-checkbox:checked + .checkmark {
  background: var(--accent);
  border-color: var(--accent);
}

.todo-checkbox:checked + .checkmark::after {
  content: "";
  display: block;
  width: 5px;
  height: 9px;
  border: 2px solid white;
  border-top: none;
  border-left: none;
  transform: rotate(45deg) translate(5px, -2px);
}

.todo-checkbox:focus-visible + .checkmark {
  box-shadow: 0 0 0 3px var(--accent-glow);
}

.todo-text {
  flex: 1;
  font-size: 0.95rem;
  word-break: break-word;
}

.btn-delete {
  display: flex;
  align-items: center;
  justify-content: center;
  background: transparent;
  border: none;
  border-radius: var(--radius-sm);
  color: var(--text-muted);
  cursor: pointer;
  padding: 0.35rem;
  opacity: 0;
  transition: color var(--transition), background var(--transition), opacity var(--transition);
  flex-shrink: 0;
}

.todo-item:hover .btn-delete,
.todo-item:focus-within .btn-delete {
  opacity: 1;
}

.btn-delete:hover {
  color: var(--danger);
  background: rgba(248, 113, 113, 0.1);
}

/* Empty state */

.empty-state {
  text-align: center;
  padding: 3rem 1rem;
  color: var(--text-muted);
}

.empty-state svg {
  margin-bottom: 1rem;
  opacity: 0.4;
}

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

/* Footer */

.footer {
  display: flex;
  align-items: center;
  justify-content: space-between;
  margin-top: 1.25rem;
  padding-top: 1rem;
  border-top: 1px solid var(--border);
}

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

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

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

/* Responsive */

@media (max-width: 400px) {
  .app {
    padding: 1.5rem 1rem 2.5rem;
  }

  .title {
    font-size: 1.6rem;
  }
}