body {
  font-family: Arial, sans-serif;
  background: #f4f4f4;
  text-align: center;
  padding: 40px;
}
h1 {
  color: #222;
}
button {
  padding: 12px 24px;
  font-size: 18px;
  background-color: #007BFF;
  color: white;
  border: none;
  border-radius: 6px;
  cursor: pointer;
}
ul {
  list-style-type: none;
  padding: 0;
  margin-top: 30px;
}
li {
  background: white;
  margin: 10px auto;
  padding: 12px;
  width: 300px;
  border-radius: 6px;
  font-size: 18px;
}
li.completed {
  text-decoration: line-through;
  color: gray;
}
li button {
  background-color: #dc3545;
  margin-left: 10px;
}