body {
  font-family: Arial, sans-serif;
  background: #f5f5f5;
  display: flex;
  justify-content: center;
  align-items: center;
  height: 100vh;
}
.container {
  background: white;
  padding: 20px;
  border-radius: 8px;
  box-shadow: 0 4px 10px rgba(0,0,0,0.1);
  width: 300px;
}
.input-box {
  display: flex;
  margin-bottom: 15px;
}
.input-box input {
  flex: 1;
  padding: 8px;
}
.input-box button {
  padding: 8px 12px;
}
ul {
  list-style: none;
  padding: 0;
}
li {
  display: flex;
  justify-content: space-between;
  padding: 6px;
  border-bottom: 1px solid #ddd;
}
li.completed {
  text-decoration: line-through;
  color: gray;
}