[DOC] Broken hyperlinks on Visualforce page

[stylishbharath]

There are broken links in the documentation : https://www.lightningdesignsystem.com/platforms/visualforce/

1. Clicking on most of the trailhead links on the documentation is causing 404 error.
2. Hyperlink for " A tool to create your custom CSS is available here " is redirecting to an unreachable page.