Text created using the package `multicols` within bookdownin RMarkdown doesn't show in html but shows in pdf?

I have a section in my book with multiple columns within bookdown in Rstudio. I added the multicolumn option by having

--- 
title: "Authoring A Book with R Markdown"
author: "Yihui Xie"
date: "`r Sys.Date()`"
site: "bookdown::bookdown_site"
output:
  bookdown::pdf_book:
    includes:
      in_header: preamble.tex
documentclass: book
bibliography: ["book.bib", "packages.bib"]
biblio-style: apalike
link-citations: yes
---

with the preamble.tex file containing

\usepackage{booktabs}
\usepackage{multicol}

I am not able to see the section I created with multicolumn in html mode (preview mode). But once I convert to pdf, I see it. Is there a reason for this? Thanks.
Any help would be appreciated.