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

 body {
     font-family: Arial, sans-serif;
     background-color: #f0f0f0;
 }

 .container {
     margin: 20px auto;
     width: 50%;
     background-color: black;
     border: 2px solid black;
     border-radius: 15px;
     color: white;
     padding: 30px;
 }

 .main {
     display: flex;
     justify-content: space-between;
     align-items: center;
     padding: 20px;
 }

 .add-input {
     padding: 8px 12px;
     font-size: 16px;
     border-radius: 8px;
     outline: none;
 }

 .btn {
     padding: 8px 20px;
     font-size: 16px;
     border-radius: 8px;
     border: none;
     background-color: lightblue;
     font-weight: 700;
     cursor: pointer;
 }

 .todo-list {
     margin-top: 20px;
     font-size: 18px;
     list-style-type: none;
 }

 .todo-item {
     display: flex;
     align-items: center;
     margin: 8px 0;
 }

 .todo-item input[type="checkbox"] {
     margin-right: 10px;
 }

 .completed {
     text-decoration: line-through;
 }