*{
  list-style: none;
}

body{
  margin-top: 30px;
}

.container{
  padding-top: 15px;
  text-align: center;
  margin: auto;
  width: 400px;
  height: 600px;
  border: black solid;
  border-radius: 15px;
  overflow: scroll;
}

.list-display{
  text-align: left;
  padding-left: 30px;
  font-size: 20px;
}

li{
  border: lightgrey solid 2px;
  margin: 1px;
  width: 250px;
  height: 100%;
  padding: 10px;
  border-radius: 15px;
}

li:hover{
  background: lightgrey;
  opacity: 0.7;
}
/*input[type=checked]{

}*/

#new-task{
  width: 300px;
  height: 40px;
  font-size: 20px;
  border-radius: 20px;
  background: lightgrey;
  padding-left: 20px;
  border: 0;
  outline: none;
}
*{
  list-style: none;
}

body{
  margin-top: 30px;
}

.container{
  padding-top: 15px;
  text-align: center;
  margin: auto;
  width: 400px;
  height: 600px;
  border: black solid;
  border-radius: 15px;
  overflow: scroll;
}

.list-display{
  text-align: left;
  padding-left: 30px;
  font-size: 20px;
}

li{
  border: lightgrey solid 2px;
  margin: 1px;
  width: 250px;
  height: 100%;
  padding: 10px;
  border-radius: 15px;
}

li:hover{
  background: lightgrey;
  opacity: 0.7;
}

.toggle:checked + label{
  text-decoration: line-through;
}
/*input[type=checked]{

}*/

#new-task{
  width: 300px;
  height: 40px;
  font-size: 20px;
  border-radius: 20px;
  background: lightgrey;
  padding-left: 20px;
  border: 0;
  outline: none;
}
Add strike-through when task is checked.
Add strike-through when task is checked.
