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代码编辑器：
<!DOCTYPE html> <style> h1.visible {visibility:visible} h1.hidden {visibility:hidden} </style> <h1 class="visible">This is a visible heading</h1> <h1 class="hidden">This is an invisible heading</h1> <p>Notice that the invisible heading still takes up space.</p> <footer>简单教程，简单编程<br/>Copyright © 简单教程 www.twle.cn</footer>
运行结果：