main.css

* {
  padding: 0;
  margin: 0;
  box-sizing: border-box;
}

body {
  font-family: cursive;
  background: #6d51a4;
}

.container {
  width: 95%;
  margin: auto;
}

.nav {
  display: flex;
  justify-content: space-between;
  flex-wrap: wrap;
  width: 100%;
  margin: 25px 0;
}

.nav h2 {
  font-size: 2em;
  color: #fff;
}

.userInputContainer {
  width: 350px;
  text-align: center;
}

.userInputContainer input {
  width: 80%;
  outline: none;
  padding: 8px;
  border: none;
  border: 1px solid #fff;
  border-top-left-radius: 5px;
  border-bottom-left-radius: 5px;
}

.userInputContainer button {
  cursor: pointer;
  padding: 8px;
  width: fit-content;
  transition: 1s;
  outline: none;
  background-color: lightgray;
  border: 1px solid #fff;
  border-top-right-radius: 5px;
  border-bottom-right-radius: 5px;
}

.userInputContainer button:hover {
  background-color: transparent !important;
  color: #fff;
}

.toDoItems {
  width: 500px;
  margin: auto;
}

.item {
  display: flex;
  justify-content: space-between;
  width: 100%;
  height: auto;
  border-radius: 2px;
  padding: 16px;
  color: #454545;
  margin-top: 10px;
  font-size: 1rem;
  text-transform: uppercase;
  transition: all .3s ease-in-out;
  background-color: #fff;
}

.item i {
  cursor: pointer;
  margin: 0 5px;
}

.item:hover {
  box-shadow: 0 0 20px #fff;
}

@media (max-width: 768px) {
  .nav {
    align-items: center;
    flex-direction: column;
  }
  .nav h2 {
    margin: 10px 0;
  }
  .userInputContainer {
    width: 100%;
  }
  .toDoItems {
    width: 100%;
  }
}

@media (main-width: 480px) {
  .userInputContainer input {
    width: 74%;
  }
}

@media (main-width: 320px) {
  .userInputContainer input {
    width: 60%;
  }
}