body {
  margin: 0;
  background-color: silver;
}
header {
  background-color: #000;
  color: #fff;
  text-align: center;
  font-family: "Rock Salt", cursive;
  font-size: 3em;
}
main {
  width: 600px;
  margin: 30px auto;
  max-width: 100%;
}
ul {
  list-style: none;
}
li {
  background-color: #fff;
  border: 2px solid #000;
  margin: 5px;
  padding: 20px;
  display: -webkit-flex;
  display: -moz-flex;
  display: -ms-flex;
  display: -o-flex;
  display: flex;
  align-items: center;
}
input {
  cursor: pointer;
/*  position: relative;
  bottom: 0.5em;*/
  margin-left: 1em;
}
input + label {
  /*display: inline;*/
  margin: 0.5em;
  font-size: 2em;
}
input:checked + label {
  text-decoration: line-through;
  color: rgba(0,0,0,0.15);
}
button {
  margin: 30px;
  cursor: pointer;
}

@media (max-width: 900px) {
  ul {
    padding: 0;
  }
}