In Rstudio rmarkdown, how to add new html themes from Bootswatch?

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Hello,

I'm building a rmarkdown file and trying to do the following

---
title: "test"
author: "test" 
output: 
    html_document:
        toc: true
        toc_float: true
        theme: solar
---

And i got the following error:

rror in match.arg(theme, themes()) : 
  'arg' should be one of "default", "cerulean", "journal", "flatly", "readable", "spacelab", "united", "cosmo", "lumen", "paper", "sandstone", "simplex", "yeti"
Calls: <Anonymous> -> <Anonymous> -> base -> match.arg

How could i add new themes?