JSFiddle - React, Tailwind, and code Playground

HTML

<div class="div_frame">

        <div class="list_title">To-Do List</div>

        <div class="list_in">
            <input class="list_input" id="list_input" type="text" placeholder="輸入代辦事項。。。">
            <button class="list_btn" onclick="add_list()">add</button>
        </div>

        <div class="list_out">

            <ul class="list_ul" id="list_ul">
                <li>
                  <span>1.倒垃圾</span>
                </li>
                <li>
                  <span>2.繳電話費</span>
                </li>
                <li>
                  <span>3.採買本週食材</span>
                </li>
            </ul>

        </div>

    </div>

CSS

.div_frame{
    width:500px;
    /*height: 500px;*/
    border-radius:20px;
    border:0;
    background-color:#fbf470;
}

.list_title{
    width: 500px;
    height: 50px;
    line-height: 50px;
    text-align: center;
    font-size: 20px;
    font-family: Comic Sans MS;

    /*border-style:solid;*/
}

.list_in{
    width: 500px;
    height: 50px;
    font-size: 20px;
    font-family: Comic Sans MS;

    display: flex;
    justify-content:center;
    align-items: center;

    /*border-style:solid;*/
}

.list_input{
    width: 300px;
    height: 30px;

    border-radius: 10px 0 0 10px;
    border:0;
    outline:none;
    
    font-family: Comic Sans MS , Microsoft JhengHei;
    text-indent: 10px;  /*輸入文字邊距*/
    transition: 0.1s;
}

.list_btn{
    width: 50px;
    height: 30px;
    box-sizing: content-box;

    border-radius: 0 10px 10px 0;
    border:0;
    
    font-family: Comic Sans MS;
    transition: 0.1s;
}
.list_btn:hover , .list_input:hover{
    box-shadow: 0px 0px 2px 2px #b1b1b1;
    z-index: 1;
}
.list_btn:active{
    box-shadow: inset 0px 0px 3px 3px #b1b1b1;
}

.list_out{
    width: 500px;
    /*height: 300px;*/
    font-size: 20px;

    font-family: Comic Sans MS , Microsoft JhengHei;

    display: flex;
    justify-content:center;

    /*border-style:solid;*/
}

.list_ul{
    list-style-type:none;   /*消除點*/
    padding-left: 0;        /*消除原本點的位置*/
}

.list_ul li{
    width: 350px;
    margin-top: 10px;       /*li之間分隔*/
    border-bottom: 1px solid #000;
    background:#ffffffa3;
}

.list_ul li span{
    font-family: Comic Sans MS , Microsoft JhengHei;
}

JavaScript

var sort = 4;       //目前清單內容數量+1

function add_list(){

    var add_text = document.getElementById('list_input').value;     //取輸入文字
    var list_ul = document.getElementById('list_ul');

    var creat_li = document.createElement('li');
    var creat_sapn = document.createElement('span');

    creat_sapn.textContent = sort.toString() + '.' + add_text;

    list_ul.append(creat_li);
    creat_li.append(creat_sapn);

    console.log(creat_sapn.textContent);
    console.log(list_ul);
    console.log(creat_li);
    sort++;
}