变量

本课属于 Coddy HTML 学习旅程的“JavaScript 实战”单元。第 21 课，共 27 课。

在这个挑战中，我们将制作一个可折叠的侧边导航菜单。目标是完成整个脚本，并添加 CSS 过渡效果，让导航菜单能够平滑地展开和收起。

挑战

简单

为菜单 div 设置 ID sideNav。
在脚本中创建三个变量：

一个用于存储侧边导航元素（sideNav）
一个用于存储打开按钮（openBtn）
一个用于存储关闭按钮（closeBtn）

亲手试试

<!DOCTYPE html>
<html>
<head>
  <title>Space Exploration</title>
  <link rel="stylesheet" href="style.css">
</head>
<body>
  <div class="sidenav">
    <button id="closeBtn" class="close-btn">&times;</button>
    <a href="#apollo">Apollo Missions</a>
    <a href="#iss">International Space Station</a>
    <a href="#mars">Mars Rovers</a>
    <a href="#jameswebb">James Webb Telescope</a>
  </div>

  <header>
    <button id="openBtn" class="open-btn">&#9776; Menu</button>
    <h1>Space Exploration</h1>
  </header>

  <main>
    <section id="apollo">
      <h2>Apollo Missions</h2>
      <p>
        The Apollo program, carried out by NASA in the 1960s and 1970s, 
        successfully landed humans on the Moon for the first time in 1969.
      </p>
    </section>

    <section id="iss">
      <h2>International Space Station</h2>
      <p>
        The ISS is a multinational research laboratory in low Earth orbit, 
        continuously inhabited since 2000 by astronauts and scientists.
      </p>
    </section>

    <section id="mars">
      <h2>Mars Rovers</h2>
      <p>
        Rovers like Spirit, Opportunity, Curiosity, and Perseverance 
        have been exploring the Martian surface, searching for signs of past life.
      </p>
    </section>

    <section id="jameswebb">
      <h2>James Webb Space Telescope</h2>
      <p>
        Launched in 2021, the James Webb Telescope is providing 
        breathtaking images of the universe and studying distant galaxies.
      </p>
    </section>
  </main>

  <script src="script.js"></script>
</body>
</html>