JSFiddle - React, Tailwind, and code Playground

HTML

<div class="wrap">
  <div class="item">
    <input type="text" id="text" placeholder="請輸入事項...">
    <select  id="select" onchange="color();">
      <option value="normal">一般</option>
      <option value="important">重要</option>
      <option value="urgent">緊急</option>
    </select>
    <a href="#" onclick="add();">新增</a> 
  </div>
  <div class="content">
    <h2>代辦事項:</h2>
    <a href="#" onclick="sumbit();">匯出</a>
    <a href="#" onclick="save()">儲存</a>
    <hr>  
  </div> 
  <ul id="event">
  </ul>
</div>

CSS

*{
  list-style: none;
  text-decoration: none;
  padding: 0;
  margin: 0;
}
.wrap{
  width: 680px;
  margin: auto;
  background-color: #FFFDD0;
}
.item{
  display: flex;
  justify-content: center;
  margin: 10px 0;
  padding-top: 10px;
}
#text{
  text-align: center;
  border: solid 1px #ccc;
  border-radius: 5px;
  margin-right: 1px;
}
a:hover{
  color:#f00;
}
#event{
  text-align: center;
}
h2{
  color: #f00;
}
li{
  margin-top: 5px;
  font-weight: bold;
  position: relative;
}
.finish-btn{
  color: #fff;
  background-color: #f00;
  padding-right: 5px;
  border-radius: 10px;
  border: none;
  text-align: center;
  padding: 0 10px;
  position: absolute;
  right: 50px;
  top:0px;   
}
li div{
  display: inline-block;
  color: green;
  display:none;
  margin-left: 10px;
}
.remove-btn{
  float: right;
  border: none;
  color: #808080;
  background-color: #FFFDD0;
  padding-right: 5px;
}
button:hover{
  color: #f00;
  cursor: pointer;
}
h2{
  text-align: center;
}
.content{
  text-align: right;
}
.content a{
  display: inline-block;
  padding: 5px;

}
select{
  border: #ccc;
  border-radius: 5px;
  margin-right: 8px;
}
.normal{
  color: #000;
}
.important{
  color: #FF6600;
}
.urgent{
  color: #f00;
}
.normal-text{
  background-color: #ccc;
}
.important-text{
  background-color:#ff6600
}
.urgent-text{
  background-color:#f00;
}
.none-text{
  background-color: #fff;
}

JavaScript

function add(){
  var text=document.querySelector("#text").value;
  if(text==""){
    alert("請輸入事項");
  }else{
    var li=document.createElement('li');  
    var span=document.createElement('span'); 
    var removeBtn=document.createElement('button'); 
    var finishBtn=document.createElement('button'); 
    var finishText=document.createElement('div'); 
    var event=document.querySelector("#event"); 
    var select=document.querySelector("#select").value 
    span.textContent=text; 
    finishBtn.textContent="標示為已完成";   
    removeBtn.textContent="刪除"; 
    finishText.textContent="(已完成)";
    
    event.append(li); 
    li.append(span);  
    li.append(finishText); 
    li.append(finishBtn);  
    li.append(removeBtn);  
    
    removeBtn.onclick=del;  
    finishBtn.onclick=finish; 
       
    li.className=select; 
    finishBtn.className='finish-btn';   
    removeBtn.className='remove-btn';
    
    var text=document.querySelector("#text"); 
    text.className="none-text"; 
    text.value="";              
  }
  function del(){
    li.remove();     
  }
}



function sumbit(){
  var spans=document.querySelectorAll("#event li span"); 
  var text="";
  var num=1;
  for(var span of spans){
    if(span.closest("li").className=="urgent"){
      text=text+" ("+num.toString()+') '+"**"+span.textContent+'**'+" "; 
    }else if(span.closest("li").className=="important"){
      text=text+"("+num.toString()+') '+"*"+span.textContent+'*'+" ";
    }else{
      text=text+" ("+num.toString()+') '+span.textContent+" ";
    }
    num++;
  }
  alert('代辦事項:'+text); 
}
function color(){
  var select=document.querySelector("#select").value;
  var text=document.querySelector("#text");
  if(select=='important'){
    text.className='important-text';
  }else if(select=='urgent'){
    text.className='urgent-text';
  }else{
    text.className='normal-text';
  }

}
function finish(){  
  var div=event.target.closest('li').querySelector('div'); 
 ...