style.css

* {
  box-sizing: border-box;
  font-family: 'Segoe UI', Tahoma, Geneva, Verdana, sans-serif;
}
body {
  margin: 0;
}
h1 {
  text-align: center;
}
.newtask {
  margin: 50px;
  display: flex;
  justify-content: center;
}
.newtask .tasktitle {
  position: relative;
  width: 75%;
  height: 70px;
}
.newtask .tasktitle::after {
  content: "";
  position: absolute;
  bottom: 0;
  left: 0;
  height: 3px;
  width: 0%;
  transition: .3s;
  background-color: #0984e3;
}
.newtask .tasktitle.fill::after {
  width: 100%;
}
.newtask .tasktitle #tasktitle {
  width: 100%;
  height: 100%;
  padding: 0 20px;
  font-size: 1.5em;
  color: #636e72;
  border: none;
  border-bottom: 1px solid #b2bec3;
  outline: none;
  cursor: pointer;
}
.newtask .tasktitle #tasktitle:focus {
  cursor: text;
}
.newtask .tasktitle #tasktitle::placeholder {
  transition: .15s;
  color: #b2bec3;
}
.newtask .tasktitle #tasktitle:focus::placeholder {
  opacity: 0;
}
.newtask #addtask {
  width: 70px;
  height: 70px;
  margin-left: 20px;
  background-color: #fefefe;
  border: 1px solid #0984e330;
  color: #0984e3;
  border-radius: 8px;
  font-size: 3em;
  font-family: fantasy;
  font-weight: bold;
  transition: .2s;
  cursor: pointer;
}
.newtask #addtask:hover {
  border-color: #0984e390;
}
.newtask #addtask.disabled {
  border: 1px solid#636e7230;
  color: #636e72;
  cursor: default;
}
hr {
  width: calc(70% + 90px);
  opacity: .3;
  margin: 64px auto;
}
.tasks {
  width: calc(70% + 90px);
  margin: auto;
}
.count {
  text-align: center;
  font-size: 1.5em;
  margin-bottom: 10px;
}
.task {
  overflow: hidden;
  background-color: #f2f2f2;
  padding: 20px;
  font-size: 2em;
  height: 86px;
  line-height: 43px;
  margin-bottom: 10px;
}
.task .title {
  float: left;
}
.task .remove, .task .done {
  float: right;
  width: 50px;
  height: 50px;
  text-align: center;
  border: 1px solid;
  cursor: pointer;
}
.task .remove {
  color: #d63031;
}
.task .done {
  margin-right: 20px;
  color: #00b894;
}
.task.done .title {
  color:#b2bec3;
  text-decoration: line-through;
}
.task.done .done {display: none}