:root {
  --bg-color: #f8fafc;
  --card-bg: #ffffff;
  --text-primary: #0f172a;
  --text-secondary: #475569;
  --primary-color: #4f46e5;
  --primary-hover: #4338ca;
  --accent-color: #3b82f6;
  --border-color: #e2e8f0;
  --shadow-sm: 0 1px 2px 0 rgb(0 0 0 / 0.05);
  --shadow-md: 0 4px 6px -1px rgb(0 0 0 / 0.1), 0 2px 4px -2px rgb(0 0 0 / 0.1);
  --shadow-lg: 0 10px 15px -3px rgb(0 0 0 / 0.1), 0 4px 6px -4px rgb(0 0 0 / 0.1);
  --radius-lg: 16px;
  --radius-md: 12px;
  --transition: all 0.3s cubic-bezier(0.4, 0, 0.2, 1);
}

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

body {
  font-family: 'Inter', system-ui, -apple-system, sans-serif;
  background-color: var(--bg-color);
  color: var(--text-primary);
  min-height: 100vh;
  display: flex;
  justify-content: center;
  align-items: center;
  padding: 2rem 1rem;
}

.app-container {
  width: 100%;
  max-width: 540px;
  background: var(--card-bg);
  border-radius: var(--radius-lg);
  box-shadow: var(--shadow-lg);
  border: 1px solid var(--border-color);
  overflow: hidden;
  display: flex;
  flex-direction: column;
}

.app-header {
  padding: 2.5rem 2rem 2rem 2rem;
  background: linear-gradient(135deg, #e0e7ff 0%, #ffffff 100%);
  border-bottom: 1px solid var(--border-color);
}

.logo-area {
  display: flex;
  align-items: center;
  gap: 0.75rem;
  margin-bottom: 0.5rem;
}

.logo-icon {
  font-size: 1.75rem;
}

.logo-area h1 {
  font-size: 1.75rem;
  font-weight: 700;
  color: var(--text-primary);
  letter-spacing: -0.025em;
}

.subtitle {
  font-size: 0.95rem;
  color: var(--text-secondary);
}

.app-main {
  padding: 2rem;
  display: flex;
  flex-direction: column;
  gap: 2rem;
}

.task-form {
  display: flex;
  gap: 0.75rem;
}

#task-input {
  flex: 1;
  padding: 0.875rem 1.25rem;
  border-radius: var(--radius-md);
  border: 1px solid var(--border-color);
  font-size: 1rem;
  outline: none;
  transition: var(--transition);
  background-color: #f1f5f9;
}

#task-input:focus {
  border-color: var(--primary-color);
  background-color: var(--card-bg);
  box-shadow: 0 0 0 3px rgba(79, 70, 229, 0.15);
}

.btn-add {
  padding: 0.875rem 1.75rem;
  background-color: var(--primary-color);
  color: white;
  border: none;
  border-radius: var(--radius-md);
  font-weight: 600;
  font-size: 1rem;
  cursor: pointer;
  transition: var(--transition);
}

.btn-add:hover {
  background-color: var(--primary-hover);
  transform: translateY(-1px);
}

.btn-add:active {
  transform: translateY(0);
}

.section-header {
  display: flex;
  justify-content: space-between;
  align-items: center;
  margin-bottom: 1rem;
}

.section-header h2 {
  font-size: 1.1rem;
  font-weight: 600;
  color: var(--text-secondary);
}

.counter {
  font-size: 0.875rem;
  background-color: #f1f5f9;
  color: var(--text-secondary);
  padding: 0.25rem 0.75rem;
  border-radius: 9999px;
  font-weight: 500;
}

.task-list {
  list-style: none;
  display: flex;
  flex-direction: column;
  gap: 0.75rem;
}

.task-item {
  display: flex;
  justify-content: space-between;
  align-items: center;
  padding: 1rem 1.25rem;
  background-color: var(--card-bg);
  border: 1px solid var(--border-color);
  border-radius: var(--radius-md);
  transition: var(--transition);
  animation: slideIn 0.3s ease-out;
}

.task-item:hover {
  border-color: #cbd5e1;
  box-shadow: var(--shadow-sm);
  transform: translateX(2px);
}

.task-content {
  display: flex;
  align-items: center;
  gap: 0.75rem;
  cursor: pointer;
}

.task-checkbox {
  appearance: none;
  width: 1.25rem;
  height: 1.25rem;
  border: 2px solid #cbd5e1;
  border-radius: 4px;
  outline: none;
  cursor: pointer;
  position: relative;
  transition: var(--transition);
}

.task-checkbox:checked {
  background-color: #10b981;
  border-color: #10b981;
}

.task-checkbox:checked::after {
  content: '✓';
  position: absolute;
  color: white;
  font-size: 0.8rem;
  font-weight: bold;
  top: 50%;
  left: 50%;
  transform: translate(-50%, -50%);
}

.task-text {
  font-size: 1rem;
  color: var(--text-primary);
  transition: var(--transition);
}

.task-item.completed .task-text {
  text-decoration: line-through;
  color: #94a3b8;
}

.btn-delete {
  background: none;
  border: none;
  color: #94a3b8;
  cursor: pointer;
  font-size: 1.25rem;
  line-height: 1;
  padding: 0.25rem;
  border-radius: 4px;
  transition: var(--transition);
}

.btn-delete:hover {
  color: #ef4444;
  background-color: #fef2f2;
}

.app-footer {
  padding: 1.5rem;
  text-align: center;
  border-top: 1px solid var(--border-color);
  font-size: 0.8rem;
  color: #94a3b8;
}

@keyframes slideIn {
  from {
    opacity: 0;
    transform: translateY(10px);
  }
  to {
    opacity: 1;
    transform: translateY(0);
  }
}