Code:

<p>该实例设置了默认显示的选项卡，在页面载入时触发指定 id 的 click 事件。</p>

<div class="tab">
    <button class="tablinks" onclick="openCity(event, 'London')" id="defaultOpen">London</button>
    <button class="tablinks" onclick="openCity(event, 'Paris')">Paris</button>
    <button class="tablinks" onclick="openCity(event, 'Tokyo')">Tokyo</button>
</div>

<div id="London" class="tabcontent">
    <h3>London</h3>
    <p>London is the capital city of England.</p>
</div>

<div id="Paris" class="tabcontent">
    <h3>Paris</h3>
    <p>Paris is the capital of France.</p>
</div>

<div id="Tokyo" class="tabcontent">
    <h3>Tokyo</h3>
    <p>Tokyo is the capital of Japan.</p>
</div>
<style>
    body {font-family: "Lato", sans-serif;}
    
    /* Style the tab */
    div.tab {
        overflow: hidden;
        border: 1px solid #ccc;
        background-color: #f1f1f1;
    }
    
    /* Style the buttons inside the tab */
    div.tab button {
        background-color: inherit;
        float: left;
        border: none;
        outline: none;
        cursor: pointer;
        padding: 14px 16px;
        transition: 0.3s;
        font-size: 17px;
    }
    
    /* Change background color of buttons on hover */
    div.tab button:hover {
        background-color: #ddd;
    }
    
    /* Create an active/current tablink class */
    div.tab button.active {
        background-color: #ccc;
    }
    
    /* Style the tab content */
    .tabcontent {
        display: none;
        padding: 6px 12px;
        border: 1px solid #ccc;
        border-top: none;
    }
</style>

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