<html><head><style>body { /* 将 "my-counter" 设置为 5 */ counter-set: my-counter 5;}h2::before { /* 将 "my-counter" 增加 1 */ counter-increment: my-counter; content: "章节 " counter(my-counter) ". ";}</style></head><body><h2>HTML 教程</h2><h2>CSS 教程</h2><h2>JavaScript 教程</h2><h2>Bootstrap 教程</h2><h2>SQL 教程</h2><h2>PHP 教程</h2></body></html>