body {
    font-family: Arial, sans-serif;
    background: #f0f8ff;
    min-height: 50vh;
    display: flex;
    justify-content: center;
    align-items: center;
    padding: 40px;
    margin: 0;
  }
  
  .container {
    background: white;
    padding: 20px 30px;
    border-radius: 10px;
    box-shadow: 0 4px 10px rgba(0,0,0,0.1);
    width: 350px;
  }
  
  h1 {
    text-align: center;
    margin-bottom: 20px;
  }
  
  .input-group {
    display: flex;
    gap: 10px;
    box-shadow: 0 4px 10px rgba(0, 0, 0, 0.1);
    border-radius: 10px;
    background-color: #fff;
    padding: 10px;
  }
  
  input[type="text"] {
    flex: 1;
    padding: 10px;
    font-size: 16px;
  }
  
  button {
    padding: 10px 15px;
    font-size: 16px;
    cursor: pointer;
  }
  
  ul {
    list-style: none;
    padding: 0;
    margin-top: 20px;
  }
  
  li {
    background: #e0f7fa;
    padding: 10px;
    margin-bottom: 10px;
    border-radius: 5px;
    display: flex;
    justify-content: space-between;
    align-items: center;
  }
  
  li.completed span {
    text-decoration: line-through;
    color: gray;
  }
  
  .btn-group button {
    margin-left: 5px;
  }