Updated several package dependencies in the `package-lock.json` file to their latest versions, including `gulp`, `@puppeteer/browsers`, and many @rollup components. Added new dependencies such as `@gulpjs/messages`, `@rollup/freebsd`, and others to expand platform support. These changes aim to maintain compatibility, security, and improved features.

Introduced additional examples for parent/child DOM traversal and event propagation, including phases like capture and bubbling. Updated index.html to reference the new `event_2.md` file, highlighting expanded content on JavaScript events.

Uncommented the Bootstrap section in the index.html file, which enables the Bootstrap section on the website. Also, added substantial content to the newly created md/html/bootstrap.md file to cover Bootstrap related materials in detail. Corrected the CSS title format in the md/html/css.md file for proper markdown rendering.