* {
  box-sizing: border-box;
  font-family: Arial, sans-serif;
}

body {
  background: #f4f4f4;
  min-height: 100vh;
  display: flex;
  justify-content: center;
  align-items: center;
}

.container {
  background: #fff;
  padding: 20px;
  width: 100%;
  max-width: 400px;
  border-radius: 8px;
}

h1 {
  text-align: center;
}

form {
  display: flex;
  gap: 10px;
  margin-bottom: 20px;
}

input {
  flex: 1;
  padding: 8px;
}

button {
  padding: 8px 12px;
  cursor: pointer;
}

ul {
  list-style: none;
  padding: 0;
}

li {
  display: flex;
  justify-content: space-between;
  align-items: center;
  padding: 8px;
  border-bottom: 1px solid #ddd;
}

li.completed {
  text-decoration: line-through;
  opacity: 0.6;
}