style.css

@import url('https://fonts.googleapis.com/css2?family=Open+Sans:wght@300;400;600&display=swap');

*{
  padding: 0;
  margin: 0;
  font-family: 'Open Sans', sans-serif;
}
body{
  display: flex;
  height: 100vh;
  justify-content: center;
  align-items: center;
  background-color: rgba(117, 73, 244,.9);
  counter-reset: li;
}
.container{
  background-color: white;
  box-shadow:  10px 10px rgba(0,0,0,.2);
  padding: 2rem 4.2rem;
  border-radius: .5rem;
}

.heading h1{
  font-size: 2rem;
  text-align: center;
  text-transform: uppercase;
  font-weight: 400;
  margin-bottom: 1.5rem;
}

.input input{
  padding: .8rem;
  padding-left: .5rem;
  line-height: .5;
  font-size: 1.4rem;
  border: none;
  border-bottom: 2px solid black;
  outline: none;
}

.tasks_container{
  margin: 3rem 0;
}

.tasks_container ul{
  list-style: none;
}

.tasks_container ul li{
  font-size: 1.2rem;
  background-color: rgba(0,0,0,.1);
  padding: 1rem;
  margin: .8rem 0;
  border-radius: .3rem;
  width: 17.3rem;
  text-overflow: ellipsis;
  overflow: hidden;
}

li::before{
  counter-increment: li;
  content: counter(li)".  ";

}

.tasks_container ul li:not(.fade-out):hover{
  text-decoration: line-through;
  cursor: pointer;
}
li.fade-out::before{
  content: '';
}
li.first::before{
  content: '';
}
.fade-out{
  color: white;
  font-weight: 600;
  text-decoration: none;
  text-align: center;
  background-color: red !important;
  opacity: .8;
  transition: background-color 300ms ease-in-out;
}
.first{
  text-align: center;
}