Fontawesome icons not showing in `bs4_book`

[bwu62]

Hey, apologies if this isn't the most relevant or informative issue report, but sometime in the past week or two it seems like some underlying style or script file used in bs4_book changed?

I'm pretty sure it's some underlying file because 3 months ago I copied the default bs4_book template and published it on a Github pages here mostly for personal use as convenient bs4_book documentation, and haven't modified it since, and it suddenly changed when I came back from a 2 week break to work on another bs4_book project.

I'm sure there are other changes, but the most significant that I noticed were the following:

• It seems like heading anchors are now broken. This was easy enough to hack back into my own project using AnchorJs and a bit of hacky jquery. It's inelegant but I can share if there's interest.
• In mobile (narrowest width) view, the TOC show/collapse button has changed styles. It no longer has several lines inside and is now just an oblong box that fills with the primary color when clicked.

I poked around the source code and developer console but couldn't figure out where the change traces to. Any help figuring out what changed and maybe how to revert it would be appreciated, thanks! :)

Edit: I checked a bunch of other bs4_books published online, including all the bookdown reference example books. All the anchor links there are broken too, in both Chrome and Firefox so I don't think it's a browser-side issue. Notably, some of the gitbook anchors still work so I think the issue is specific to something in the bs4_book template.