style.css

* {
  margin: 0;
  padding: 0;
  box-sizing: border-box;
}
.main {
  min-width: 70%;
  max-width: 90%;
  max-height: 300px;

  padding: 20px 10px;
  background-color: #ddd;
  border-radius: 9px;
  -webkit-border-radius: 9px;
  -moz-border-radius: 9px;
  -ms-border-radius: 9px;
  -o-border-radius: 9px;
  display: flex;
  flex-wrap: wrap;
  justify-content: space-between;
  overflow-x: hidden;
  overflow-y: scroll;
  position: absolute;
  top: 40%;
  left: 50%;
  transform: translate(-50%, -50%);
  -webkit-transform: translate(-50%, -50%);
  -moz-transform: translate(-50%, -50%);
  -ms-transform: translate(-50%, -50%);
  -o-transform: translate(-50%, -50%);
}
.main::-webkit-scrollbar {
  width: 0.5rem;
}

.main::-webkit-scrollbar-track {
  background: gray;
}

.main::-webkit-scrollbar-thumb {
  background: red;
}
.main input {
  width: 80%;
  border: none;
  outline: none;
  padding: 10px;
}
.main > button {
  width: 19%;
  padding: 10px;
  border-radius: 9px;
  -webkit-border-radius: 9px;
  -moz-border-radius: 9px;
  -ms-border-radius: 9px;
  -o-border-radius: 9px;
  color: white;
  background-color: red;
  cursor: pointer;
}
.main input,
.main > button {
  height: 40%;
  margin-top: 10px;
  border: none;
  outline: none;
}
.task {
  width: 99%;
  padding: 10px;
  background-color: #eee;
  border-radius: 9px;
  -webkit-border-radius: 9px;
  -moz-border-radius: 9px;
  -ms-border-radius: 9px;
  -o-border-radius: 9px;
  margin: 5px 0;
  display: flex;
  justify-content: space-between;
}
.task > button {
  border-radius: 9px;
  -webkit-border-radius: 9px;
  -moz-border-radius: 9px;
  -ms-border-radius: 9px;
  -o-border-radius: 9px;
  color: white;
  text-align: center;
  padding: 5px;
  background-color: red;
  border: none;
  outline: none;
  cursor: pointer;
}