Error in running a bookdown - demo : "no package called ‘ htmltools ’"

Question

I tried to run a bookdown-demo example and I got an error message. I did the following:

1. I downloaded and unzipped the folder https://github.com/rstudio/bookdown-demo.

2. I started the test_bookdown.Rproj as a project within RStudio, opened the index.Rmd file, and clicked on the Knit button. I got a pdf output in the view window and an output PDF file in the folder _book/bookdown-demo.pdf. (It was not the html output as in the tutorial at https://bookdown.org).

3. When I tried to compile the book by pressing the Build Book button within the RStudio Build pane, I got the following error message:

Error in loadNamespace(i, c(lib.loc, .libPaths()), versionCheck = vI[[i]]) : there is no package called ‘htmltools’ Calls: :: ... tryCatch -> tryCatchList -> tryCatchOne -> Execution halted

Exited with status 1.

Could anyone, please, help me to resolve the issue? Thank you in advance.