* {
  box-sizing: border-box;
}

body {
  background: #f0f2f5;
  font-family: Arial, sans-serif;
  display: flex;
  align-items: center;
  justify-content: center;
  height: 100vh;
  margin: 0;
}

.container {
  background: #fff;
  padding: 20px 30px;
  border-radius: 8px;
  box-shadow: 0 2px 8px rgba(0,0,0,0.1);
  width: 100%;
  max-width: 400px;
}

h1 {
  text-align: center;
  margin-bottom: 20px;
  color: #333;
}

.input-group {
  display: flex;
  margin-bottom: 20px;
}

#new-todo {
  flex: 1;
  padding: 10px;
  border: 1px solid #ddd;
  border-radius: 4px 0 0 4px;
  outline: none;
}

#new-todo:focus {
  border-color: #5b9bd5;
}

#add-btn {
  padding: 10px 20px;
  border: none;
  background: #5b9bd5;
  color: #fff;
  cursor: pointer;
  border-radius: 0 4px 4px 0;
}

#add-btn:hover {
  background: #4a8ac2;
}

ul#todo-list {
  list-style: none;
  padding: 0;
  margin: 0;
}

ul#todo-list li {
  padding: 10px;
  border-bottom: 1px solid #eee;
  display: flex;
  align-items: center;
  justify-content: space-between;
}

ul#todo-list li.completed {
  text-decoration: line-through;
  color: #888;
}

ul#todo-list li button.remove-btn {
  background: none;
  border: none;
  color: #ff5b5b;
  cursor: pointer;
  font-size: 16px;
}