JSFiddle - React, Tailwind, and code Playground

HTML

<body>
    <div id="todo-header-box">
        <h2>TODO</h2>
        <input type="text" id="my-input" placeholder="Add new..."> <span id="new-btn">Add</span>
        <br>
        <br>
    </div>
    <div id="todo-body-box">
        <ul id="my-todo-list">

        </ul>
    </div>
    <h1 id="h"></h1>
    <script src="script.js"></script>
</body>

CSS

* {
    box-sizing: border-box;
}

html {
    background: royalblue;
}

body {
    width: 50%;
    margin: auto;
}

ul {
    margin: 0;
    padding: 0;
    list-style-type: none;
}

ul li {
    cursor: pointer;
    position: relative;
    padding: 15px 10px 15px 40px;
    text-align: left;
    transition: 0.2s;
    font-size: 20px;
    color: #f5f5f5;
    /* make the list items unselectable */
    -webkit-user-select: none;
    -moz-user-select: none;
    -ms-user-select: none;
    user-select: none;
}

li:nth-child(even) {
    background: #555;
}

li:nth-child(odd) {
    background: #777;
}

#todo-header-box,
#todo-body-box {
    width: 100%;
    margin: 0 auto;
    text-align: center;
}

#todo-body-box {
    border: 2px solid #f5f5f5;
}

#todo-header-box {
    border-right: 2px solid #f5f5f5;
    border-left: 2px solid #f5f5f5;
    border-top: 2px solid #f5f5f5;
    padding: 10px;
    background: #2d2d2d;
    margin-top: 100px;
}

#my-input {
    padding: 5px;
    width: 80%;
    font-size: 20px;
    border: 2px solid #f5f5f5;
}

#new-btn {
    background: #00a86b;
    padding: 6px 20px;
    color: #f5f5f5;
    font-size: 23px;
    position: relative;
    right: 4px;
    border: 1px solid #f5f5f5;
    cursor: pointer;
}

#new-btn:hover {
    background: rgba(0, 168, 107, 0.7);
}

h2 {
    font-size: 30px;
    color: #f5f5f5;
    text-decoration: underline;
    text-align: center;
}

li:hover {
    background: #bbb;
}

ul li.checked {
    text-decoration: line-through;
    background: #000;
}

.closeBtn {
    position: absolute;
    top: 0;
    right: 0;
    padding: 15px 25px;
}

.closeBtn:hover {
    background: #00a86b;
    background: indianred;
}

JavaScript

/*   
  TODO REQUIRE:
        Remove items from ToDoList  -   Remove the correct item
        Why can't handle if empty
        Make the code more Clean - Remove repeating code
 */
function getTodoItems() {
    for (var i = 0; i < dataArray.length; i++) {
        if (!dataArray[i].listItem.length) return;
        var itemList = document.getElementById("my-todo-list");
        var list = document.createElement("li");
        itemList.appendChild(list);
        list.innerHTML = dataArray[i].listItem;
        var spanItem = document.createElement('span');
        spanItem.style.float = 'right';
        var myCloseSymbol = document.createTextNode('\u00D7');
        spanItem.classList.add("closeBtn");
        spanItem.appendChild(myCloseSymbol);
        listItems[i].appendChild(spanItem);
        close[i].onclick = function(e) {
            var div = e.target.parentElement;
            div.style.display = "none";
            var position = dataArray.findIndex(item => item.listItem === div.childNodes[0].nodeValue);
            dataArray.splice(position, 1); // Fix denne her linje
            localStorage.setItem("itemListRecord", JSON.stringify(dataArray));
        }
        var list = document.getElementsByTagName('li');
        list[i].onclick = function() {
            this.classList.toggle("checked");
        }

    }
}
var keyAdd = false;
// Data Object
var dataArray = JSON.parse(localStorage.getItem("itemListRecord")) || new Array();

// Add Close Button to <li></li> element
var listItems = document.getElementsByTagName('li');
for (var i = 0; i < listItems.length; i++) {
    var spanItem = document.createElement('span');
    spanItem.style.float = 'right';
    var myCloseSymbol = document.createTextNode('\u00D7');
    spanItem.classList.add("closeBtn");
    spanItem.appendChild(myCloseSymbol);
    listItems[i].appendChild(spanItem);
}

// Remove <li></li> element from the list
var close = document.getElementsByClassName("closeBtn");
for (var i = 0; i <...