JSFiddle - React, Tailwind, and code Playground

HTML

<div class="container">
  <div class="input-wrap">
    <input class="input" type="text">
    <select class="task">
      <option value="normal">一般</option>
      <option value="important">重要</option>
      <option value="urgent">緊急</option>
    </select>
    <button class="new-btn">新增</button>
  </div>
  
  <ul class="lists">
    <li class="list-title"><span>代辦事項</span><button class="export">匯出</button></li>
  </ul>
  
</div>

SCSS

* {
  box-sizing: border-box;
}

.container {
  max-width: fit-content;
  margin: 30px auto;
  
  .input-wrap {
    display: flex;
    align-items: center;

    
    .input {
      border-top-left-radius: 8px;
      border-bottom-left-radius: 8px;
      font-size: 2rem;
      height: 2.5rem;
      padding: 10px;
      background-color: #aaa;
      max-width: fit-content;
      border: none;
      outline: none;
      transition: background-color 0.5s;
      
      &.important {
        background-color: #fa0;
        
        & + .task {
          background-color: #fa0;
        }
        
        & ~ .new-btn {
          background-color: #fa0;
        }
      }
      
      &.urgent {
        background-color: #f00;
        
        & + .task {
          background-color: #f00;
        }
        
        & ~ .new-btn {
          background-color: #f00;
        }
      }
    }
    
    .task {
      height: 2.5rem;
      border: none;
      outline: none;
      background-color: #aaa;
      border-right: 1px solid #000;
      border-left: 1px solid #000;
      cursor: pointer;
      font-size: 18px;
      font-weight: bold;
      transition: color, background 0.5s;
      
      
      &:hover {
        color: #fff;
      }
    }

    .new-btn {
      height: 2.5rem;
      background-color: #aaa;
      border-top-right-radius: 8px;
      border-bottom-right-radius: 8px;
      border: none;
      white-space: nowrap;
      cursor: pointer;
      font-weight: bold;
      font-size: 18px;
      color: #fff;
      transition: color, background 0.5s;
      
      &:hover {
        color: #000;
      }
    }
  }
  
  .lists {
    margin-top: 20px;
    background-color: #aaa;
    border-radius: 8px;
    padding: 0 10px 10px 10px;
    
    .list {
      background-color: #ccc;
      font-size: 24px;
      padding: 5px 10px;
      border-radius: 8px;
      height: 2.5rem;
      display: flex;
      justify-content: space-between;
      
      &.important {
       ...

JavaScript

const input = document.querySelector('.input');
const lists = document.querySelector('.lists');
const newButton = document.querySelector('.new-btn');
const exports = document.querySelector('.export');
const task = document.querySelector('.task');

function inputInitClass() {
	input.classList.remove('important');
  input.classList.remove('urgent');
}

function add() {
	let todoText = input.value;
  let taskValue = task.value;
  
  if (todoText.trim() === '') return;
  
  let list = document.createElement('li');
  let span = document.createElement('span');  
  let deleteButton = document.createElement('button');
  
  list.classList.add('list');  
  span.textContent = todoText;
  deleteButton.classList.add('del-btn');
  deleteButton.textContent = '刪除';
  deleteButton.onclick = remove;
  
  if (taskValue === 'important') {
    list.classList.add('important');
  } else if (taskValue === 'urgent') {
    list.classList.add('urgent');
  }
  
  lists.append(list);
  list.append(span);
  list.append(deleteButton);

  document.querySelector('.input').value = '';
  document.querySelector('.task').value = 'normal';
  inputInitClass();
}

function remove() {
	event.target.parentElement.remove();
}

function exportArray() {
	let result = '';
  if (lists.children.length < 2) return alert('無代辦事項');

	for (let i = 1; i < lists.children.length; i++) {
    let todo = lists.children[i].children[0].textContent;
    let taskCategory = lists.children[i].className.split(' ')[1];
    
    if (taskCategory === 'important') {
      result += `${i}. *${todo}* `;
    } else if (taskCategory === 'urgent') {
      result += `${i}. **${todo}** `;
    } else {
      result += `${i}. ${todo} `;
    }
  }
  alert(`今日待辦：${result}`);
}

function change() {
	let targetValue = event.target.value;
	if (targetValue === 'important') {
    input.classList.remove('urgent');
    input.classList.add('important');
  }
  
  if (targetValue === 'urgent') {
  	input.classList.remove('important');
   ...