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

body {
  font-family: 'Segoe UI', Tahoma, sans-serif;
  background: linear-gradient(135deg, #667eea 0%, #764ba2 100%);
  min-height: 100vh;
  padding: 20px;
}

.container {
  max-width: 500px;
  margin: 0 auto;
  background: white;
  border-radius: 16px;
  padding: 30px;
  box-shadow: 0 20px 60px rgba(0,0,0,0.3);
}

h1 {
  text-align: center;
  color: #333;
  margin-bottom: 25px;
  font-size: 28px;
}

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

#todoInput {
  flex: 1;
  padding: 14px 18px;
  border: 2px solid #e0e0e0;
  border-radius: 10px;
  font-size: 16px;
  transition: border-color 0.3s;
}

#todoInput:focus {
  outline: none;
  border-color: #667eea;
}

#addBtn {
  padding: 14px 24px;
  background: linear-gradient(135deg, #667eea 0%, #764ba2 100%);
  color: white;
  border: none;
  border-radius: 10px;
  font-size: 16px;
  font-weight: 600;
  cursor: pointer;
  transition: transform 0.2s, box-shadow 0.2s;
}

#addBtn:hover {
  transform: translateY(-2px);
  box-shadow: 0 5px 20px rgba(102, 126, 234, 0.4);
}

.filters {
  display: flex;
  gap: 8px;
  margin-bottom: 20px;
}

.filter {
  flex: 1;
  padding: 10px;
  background: #f5f5f5;
  border: none;
  border-radius: 8px;
  cursor: pointer;
  font-size: 14px;
  transition: all 0.2s;
}

.filter.active {
  background: linear-gradient(135deg, #667eea 0%, #764ba2 100%);
  color: white;
}

.filter:hover:not(.active) {
  background: #e0e0e0;
}

#todoList {
  list-style: none;
  margin-bottom: 20px;
}

.todo-item {
  display: flex;
  align-items: center;
  gap: 12px;
  padding: 15px;
  background: #f9f9f9;
  border-radius: 10px;
  margin-bottom: 10px;
  animation: slideIn 0.3s ease;
}

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

.todo-item.completed {
  background: #e8f5e9;
}

.todo-item.completed .todo-text {
  text-decoration: line-through;
  color: #888;
}

.checkbox {
  width: 24px;
  height: 24px;
  border: 2px solid #667eea;
  border-radius: 50%;
  cursor: pointer;
  display: flex;
  align-items: center;
  justify-content: center;
  transition: all 0.2s;
  flex-shrink: 0;
}

.checkbox:hover {
  background: rgba(102, 126, 234, 0.2);
}

.todo-item.completed .checkbox {
  background: #4caf50;
  border-color: #4caf50;
}

.checkbox::after {
  content: '✓';
  color: white;
  font-size: 14px;
  display: none;
}

.todo-item.completed .checkbox::after {
  display: block;
}

.todo-text {
  flex: 1;
  font-size: 16px;
  color: #333;
}

.delete-btn {
  background: none;
  border: none;
  color: #ff6b6b;
  font-size: 20px;
  cursor: pointer;
  opacity: 0.5;
  transition: opacity 0.2s;
}

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

.stats {
  display: flex;
  justify-content: space-between;
  align-items: center;
  padding-top: 15px;
  border-top: 1px solid #eee;
  font-size: 14px;
  color: #666;
}

#clearCompleted {
  padding: 8px 16px;
  background: #ff6b6b;
  color: white;
  border: none;
  border-radius: 8px;
  cursor: pointer;
  font-size: 14px;
  transition: background 0.2s;
}

#clearCompleted:hover {
  background: #ff5252;
}

.empty-state {
  text-align: center;
  color: #888;
  padding: 40px;
  font-size: 16px;
}