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

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

.container {
  max-width: 500px;
  margin: 50px auto;
  background: white;
  border-radius: 15px;
  padding: 30px;
  box-shadow: 0 10px 40px rgba(0, 0, 0, 0.2);
}

h1 {
  text-align: center;
  color: #333;
  margin-bottom: 25px;
  font-size: 2rem;
}

.input-group {
  display: flex;
  gap: 10px;
  margin-bottom: 25px;
}

#todo-input {
  flex: 1;
  padding: 12px 15px;
  border: 2px solid #e0e0e0;
  border-radius: 8px;
  font-size: 1rem;
  outline: none;
  transition: border-color 0.3s;
}

#todo-input:focus {
  border-color: #667eea;
}

#add-btn {
  padding: 12px 25px;
  background: linear-gradient(135deg, #667eea 0%, #764ba2 100%);
  color: white;
  border: none;
  border-radius: 8px;
  font-size: 1rem;
  cursor: pointer;
  transition: transform 0.2s, box-shadow 0.2s;
}

#add-btn:hover {
  transform: translateY(-2px);
  box-shadow: 0 5px 15px rgba(102, 126, 234, 0.4);
}

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

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

.todo-item {
  display: flex;
  align-items: center;
  padding: 15px;
  background: #f8f9fa;
  border-radius: 8px;
  margin-bottom: 10px;
  transition: all 0.3s;
}

.todo-item:hover {
  background: #f0f0f0;
}

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

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

.todo-checkbox {
  width: 22px;
  height: 22px;
  margin-right: 12px;
  cursor: pointer;
  accent-color: #4caf50;
}

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

.delete-btn {
  background: #ff5252;
  color: white;
  border: none;
  padding: 6px 12px;
  border-radius: 5px;
  cursor: pointer;
  font-size: 0.85rem;
  transition: background 0.3s;
}

.delete-btn:hover {
  background: #ff1744;
}

.stats {
  text-align: center;
  padding: 15px;
  background: #f5f5f5;
  border-radius: 8px;
  color: #666;
  font-size: 0.9rem;
}

@media (max-width: 600px) {
  .container {
    margin: 20px;
    padding: 20px;
  }
  
  h1 {
    font-size: 1.5rem;
  }
  
  .input-group {
    flex-direction: column;
  }
  
  #add-btn {
    width: 100%;
  }
}