Make websites with R Markdown styled with the GOV.UK Design System. See the website. Please also consider an alternative, govuk-hugo-r.

remotes::install_github("ukgovdatascience/govdown")

If you are developing a Shiny application, then look at https://github.com/moj-analytical-services/shinyGovstyle.

Use install-govuk-frontend.sh to download, modify and compile the GOV.UK Design System to get the css files for the templates.

The sassc command-line tool. If you can't get that to work, try the sass package by RStudio, which wraps it.