body {
  color: #555;
  font-size: 1.25em;
  font-family: 'Helvetica Neue', Helvetica, Arial, sans-serif;
}

.container {
  margin: 40px auto;
  max-width: 700px;
}

input[type = "checkbox"]:checked + label {
  text-decoration: line-through;
  color: grey;
}