JSFiddle - React, Tailwind, and code Playground

HTML

<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
</head>
<body>
  <div class="wrap">
    <div class="item">
    <input type="text"    id="content">
   <button onclick="addNew()">Add</button>
    </div>
  </div>
  
  <div class="wrap wrap_task">
    <h1>代辦清單</h1>
    <ul id="task"></ul>
  </div>
  
</body>
</html>

CSS

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



span{
  font-size:30px;
  font-size:600;
  color:#6A381F;
}

html,body{
  width:100%;
  height:100%;
  background-color:#6E0D25;
}

.wrap{
  background-color:#FFFFB3;
 padding:2rem;
 margin:2rem;
 display:flex;
 justify-content:center;
 border-radius:20px;
}


.wrap_task{
  flex-direction:column;
  align-items:center;
}

JavaScript

function addNew(){
  let content = document.getElementById("content").value;
  let ul = document.getElementById("task");
  let li = document.createElement("li");
  let sp = document.createElement("span");
  
  ul.appendChild(li).appendChild(sp).append(content);
}